RAM module build - part 3

Summary

In this video, the presenter enhances a 16-bit RAM module by integrating an address register and 74 LS157 chips, enabling data input from DIP switches or a bus. They demonstrate setting memory addresses with switches and writing data into memory using a push button. The setup allows toggling between programming and run modes, with an AND gate combining control and clock signals for memory writes during run mode. The video concludes with a setup overview, promising further testing in the next installment.

Takeaways

• 💾 The video discusses augmenting a 16-bit RAM module with an address register to facilitate memory management.
• 🔄 It explains the process of switching between address register and programming mode using DIP switches.
• 🔌 The presenter demonstrates connecting 8 bits of data to either the bus or DIP switches using 74LS74 series chips.
• 🛠️ Additional breadboarding is used to accommodate the growing complexity of the computer's circuitry.
• 🔩 The video covers the connection of power and ground for the 74LS157 chips, which are used for data input selection.
• 🔄 The strobe input (pin 15) is connected to ground to enable the chip, which is crucial for the operation of the memory module.
• 🔗 Outputs from the 74LS157 chips are directed to the data inputs of the memory, allowing data to be written into memory.
• 🔑 DIP switches are used to set data values for memory programming, with the state of the switch determining the data input (0 or 1).
• 🔲 The video also addresses the need to switch between programming mode (using DIP switches) and run mode (using bus data).
• 🔄 A 74LS157 chip is used to select the write signal source, either from a push button in programming mode or from control logic in run mode.
• 🕒 The write operation is synchronized with the clock signal using a NAND gate to ensure data is written on the rising edge of the clock cycle.

Q & A

What is the primary purpose of augmenting the 16-bit RAM module with an address register?

The primary purpose is to enable switching between the address register and the programming mode, allowing the setting of the address with DIP switches and viewing the memory contents.

How does the use of 74LS74 chips help in the memory storage process described in the script?

The 74LS74 chips are used to switch between the DIP switches and the bus for the data being stored in memory, allowing the selection of data input sources for memory storage.

What is the significance of the strobe input connected to ground in the context of the 74LS157 chips?

The strobe input connected to ground acts as an enable line for the 74LS157 chips, ensuring that the chips are enabled and functioning when the strobe input is low.

Why are two 74LS157 chips needed for the eight-bit data handling in this setup?

Two 74LS157 chips are needed because each chip handles four bits, and with eight bits of data to manage, two chips are required to cover all data inputs.

How are the DIP switches used to program the memory in the described setup?

The DIP switches are used to set the data values that are written into memory when in programming mode. The switches connect the A inputs of the 74LS74 chips to ground when on, representing the data to be stored.

What is the role of the push button in the memory programming process?

The push button is used to trigger the write operation, allowing data set on the DIP switches to be written into the memory at the address set by the address register.

How does the script differentiate between programming mode and run mode for memory operations?

Programming mode is indicated by the use of DIP switches for data input and a push button for write signals, while run mode uses data from the bus and control signals from the computer's control logic.

What is the function of the 74LS00 NAND gate in the context of the memory write signal?

The 74LS00 NAND gate is used to combine the control signal and the clock signal to determine when to write data into memory, ensuring that the write operation occurs on the rising edge of the clock.

Why is the write signal from the control logic combined with the clock signal?

The write signal from the control logic is combined with the clock signal to synchronize the write operation with the system's clock, ensuring that data is written to memory at the correct time during the system's operation.

What is the purpose of the select pins on the 74LS74 chips in the script?

The select pins on the 74LS74 chips are used to determine whether the system is in programming mode or run mode, switching the input sources for data accordingly.

Outlines

00:00

💻 Enhancing RAM Module with Address and Data Input

The video begins with a continuation from the previous one, where the presenter has augmented a 16-bit RAM module with an address register. The aim is to allow switching between the address register and programming mode using DIP switches to set the address. The presenter plans to connect the data bits of the RAM to either take data from the bus or from DIP switches, similar to the address register setup. To achieve this, 74LS74 chips are used to switch between the DIP switches and the bus for data storage. The presenter adds another breadboard for more room and connects the instruction register from a previous video, not for immediate use but for future integration. The 74LS157 chips are introduced for selecting between the A and B inputs, with the strobe input connected to ground to enable the chip. The outputs of these selectors are then connected to the data inputs of the memory, allowing for data programming from the DIP switches or data input from the bus.

05:00

🔌 Wiring DIP Switches and Bus for Data Input

The presenter proceeds to connect the DIP switches to the A inputs of the 74LS74 chips, allowing the setting of data values when in programming mode. The switches are wired such that when on, they connect to ground, setting a low logic level, and when off, they default to high due to the internal pull-up resistors. The presenter also connects the bus to the B inputs of the 74LS74 chips, enabling data to be written into memory from the bus during normal operation. The video details the process of setting up the wiring for both programming and run modes, including the use of a push button for writing data to memory in programming mode. The presenter also discusses the need for a control signal to write data into memory, which will be managed by another 74LS157 chip, and the use of a NAND gate to combine the control signal and the clock signal for memory writing in run mode.

10:00

🔧 Finalizing RAM Module Setup and Testing

In the final part of the video, the presenter focuses on the final connections and setup of the RAM module. The right signal, which controls writing to memory, is sourced from a selector using a 74LS157 chip. The presenter explains the need to combine the right signal with the clock signal using a NAND gate to ensure that writing to memory occurs on the rising edge of the clock. The presenter connects the necessary power and ground for the NAND gate and hooks up the control signal and clock signal to the inputs of the gate. The setup is then tested, with the presenter noting the need to connect the select pins for all the 74LS74 chips to ensure they operate correctly in both programming and run modes. The video concludes with the presenter preparing to power up the system and test it more thoroughly in the next video.

Keywords

💡Address Register

An address register is a type of storage register in a computer system that holds the memory address of data or instructions. In the context of the video, the address register is augmented with a 4-bit address register to allow switching between the address register and programming mode, enabling the setting of the address with DIP switches. This is crucial for accessing and manipulating specific locations in memory during the programming of the computer.

💡DIP Switches

DIP switches, or dual inline package switches, are a type of user interface for electronic devices that allow for manual configuration of settings. In the video, DIP switches are used to set the address and data values for programming the computer's memory. They provide a physical means to input values directly into the system, which is essential for initial programming before the computer operates autonomously.

💡Memory Contents

Memory contents refer to the data stored in a computer's memory. The video discusses the connection of 8 bits to the memory, which initially appear to be set to ones, but are intended to be connected to an input source for data storage. Understanding memory contents is key to grasping how data is written to and read from memory during the computer's operation.

💡74LS74

The 74LS74 is a type of integrated circuit, specifically a dual positive-edge triggered flip-flop. In the video, 74LS74 is mentioned in the context of switching between DIP switches and the bus for data storage in memory. It plays a critical role in the data input/output process, allowing the system to select between different data sources based on the mode of operation.

💡Bus

A bus in computer terminology refers to a shared communication path that allows different parts of a computer to exchange data. In the video, the bus is mentioned as a pathway for data to be stored in memory or read from it. It's an essential component for the transfer of information within the computer system, particularly during the normal operation mode when the computer is not being programmed manually.

💡Programming Mode

Programming mode is a state in which a computer system is configured to receive and store instructions or data manually. In the video, the process of switching to programming mode allows the user to set addresses and data using DIP switches, which is necessary for loading a program into the computer's memory before execution.

💡Instruction Register

An instruction register is a type of register that holds the current instruction being executed by the computer's processor. Although not directly utilized in the context of the video, the instruction register is mentioned as a component that will be placed in the computer setup, indicating its importance in the overall architecture of the computer for holding and executing instructions.

💡74LS157

The 74LS157 is a multiplexer integrated circuit that selects one of several input lines and routes it to a single output line. In the video, two 74LS157 chips are used to switch between the DIP switches and the bus for data input into memory. This selection process is vital for determining whether data comes from the user's manual inputs (DIP switches) or from the computer's internal data flow (bus).

💡Strobe Input

A strobe input is a signal used to synchronize data transmission, often used to latch data at a specific time. In the video, the strobe input connected to ground acts as an enable line for the 74LS157 chip, allowing the chip to function when the strobe signal is low. This is an important aspect of controlling the timing of data input into the memory.

💡Tri-State Buffers

Tri-state buffers are digital circuits that can have three output states: high, low, or high-impedance (off). In the video, these buffers are mentioned in the context of reading data from memory and sending it to the bus. They are crucial for managing data flow and preventing conflicts on the bus by disabling the output when not in use.

💡Control Logic

Control logic refers to the part of a computer system that controls the operation of the processor, determining the sequence of instructions and managing the flow of data. In the video, the control logic is mentioned as a future component that will provide signals to write data into memory during the computer's run mode, indicating its role in the computer's operational control.

Highlights

Augmentation of the 16-bit RAM module with a 4-bit address register for address setting using DIP switches.

Introduction of a mechanism to switch between address register and programming mode for memory address setting.

Connection of 8 bits to an input for data storage in memory, either from the bus or DIP switches.

Utilization of 74LS74 series for switching between DIP switches and bus data for memory storage.

Expansion of the breadboard setup to accommodate additional components like the instruction register.

Explanation of the strobe input's role as an enable line for the 74LS157 chip.

Connection of the outputs of the selectors to the data inputs of memory for data writing.

Setup of DIP switches to connect the A inputs of the 74LS74 chips to ground when a switch is on.

Inversion of switch logic to match the intuitive understanding of on (connected to ground) and off (disconnected).

Connection of the bus to the B inputs of the 74LS157 chips for normal run mode data writing.

Description of the programming process involving setting an address and data, then writing to memory using a push button.

Use of another 74LS157 chip to switch between the push button and control logic signals for memory writing.

Discussion on the necessity of synchronizing the write signal with the clock signal using a NAND gate.

Connection of the NAND gate to create a conditional write signal based on the control signal and the clock.

Final setup and testing of the RAM module with the new programming and write capabilities.

Anticipation of future videos detailing the control logic and its integration with the memory writing process.

Transcripts

so in the last video we augmented our 16

by Ram module with an address register a

4-bit address register uh that we can

then switch between the address register

and our programming mode which allows us

to set the address with these dip

switches and we can see the address here

and we can see the memory contents here

in this video what I want to do is do

something similar for the the actual

data that we're storing in memory so

right now we have these eight bits which

right now I've just connected down here

to looks like they're all set to ones

but instead we want to connect these uh

to to some uh sort of input that's

either going to take the data to store

off the bus or uh take it from dip

switches so very similar to this and so

again we're going to use the 74 ls7s to

switch between um the dip switches and

the bus for the data that we're storing

in memory and so again we want to give

ourselves a little bit more room so

going to use another breadboard here and

I'm going to connect it right here

because we're going to do this right

below here now actually I'm also going

to connect below this the um uh

instruction register which we built in a

previous video uh and we're not really

going to be using the instruction

register at all for this but um just

when we put the final computer together

this is a good place for it so we'll

just we'll just have that there so like

I said what we want is we want some dip

switches here when we're in programming

mode we'll be able to set the address

here we'll be able to set the data here

uh to write data into memory um and

that's how we get our program into

memory before we actually start running

uh things on the computer and then to

switch between uh using the switches to

program the computer and uh actually

being able to let the computer put

things in its memory on its own from the

bus we want to use those 74 LS 157 uh

chips that we that we looked at in the

last video um so it has these A and B

inputs and a y output and and you select

between A and B using this select uh pin

here since we have eight bits here

instead of the four um instead of using

one of these chips we'll we'll need two

and we'll start of course by hooking up

the power and ground for each of these

chips and then uh just as we did up here

we have this uh pin 15 which is the

strobe input connected to ground um and

that's essentially just kind of an

enable line for the whole chip so uh

whenever that's low the chip is enabled

so I'll go ahead and connect

pin 15 here to ground and this one's

going to be a little bit tricky cuz I

have these LEDs in the way but let me

pull this out for a moment and we can

kind of slide that

in and put the LED back in there

hopefully in the right

place okay so that's hooked up and then

next what I'm going to do is I'm going

to connect the outputs got four lines on

on each of these we have total of eight

lines that we're selecting between

either the dip switches or uh well it'll

be the bus that we end up connecting

into the uh the B and puts here uh but

first I'll start with connecting the

outputs of these into the the the data

inputs of our memory so that whichever

Source we're selecting from the output

is going to go into our memory so we're

writing that that bite into

memory okay so I think that is

everything so we can pull these

out and now all of

the outputs of our of our selectors uh

should be going to the data inputs of

our memory so we should be able able to

well once we hook up our dip switches

and our bus we should EI either be able

to program the memory from the Dip

switches or you know data coming in from

the bus should be able to find its way

into the memory so now to hook up the

dip switches it's going to be very

similar to what we did up here which is

we're going to be using the dip switches

to connect the in the a inputs on both

of these to ground when the switch is on

uh so for

example this will connect the a input of

this

first uh this first bit or the sort of

the most significant bit here to ground

when the switch is on and of course for

that to work I need to connect this side

of it to

ground so when that's on then it

connects ground to that input and then

when it's off it's disconnected uh which

means that the input's going to default

to high because all of the inputs on

these on these have a pull-up resistors

built into these chips if it's not

connected the input will be High um and

again just like we did here uh because

it's kind of unintuitive for the switch

to be down meaning high and up meaning

uh zero or so down is a one up is a zero

um I'm going to just flip this switch

upside down so that way

when the switches are down they're on

and then when we flip the switch up the

switch turns off and so when it's off

it's not connected to ground which means

it's going to be a one and when it's on

when it's down it is connected to ground

and it's a zero so I'll go ahead and

connect the the rest of

these and of course for these inputs up

here then I'll just connect the uh

connect them through the switch the

other way connect the grounds down here

and then they just connect up into these

pins up here rather than trying to run

the wires back and

forth okay and that should be connecting

our dip switches up to the a inputs of

of the 74

ls7s now the B inputs of the 74 ls7s so

so the a inputs are when we're in uh

programming mode so in programming mode

we set our address here we set our um

our data value here and then we can

write using this signal and it'll hook

up a a push button for this in a in a

moment uh use this signal to put

whatever uh value we set here into the

address uh that we set here and that's

how we program the computer that's how

we put data into the into the memory

before we start the computer when we go

into run mode then uh when we want to

write data into the memory it's going to

be coming from the bus and the bus and

then when we when we want to read data

from memory it goes out to the bus

through these Tri-State buffers but to

get data in from the bus um we want to

bring that down into the B inputs of our

74 LS 157 our our selectors here so I'm

going to go ahead head and hook that up

now okay so that now connects the bus

which which is going to be connected

here uh on these eight bits that that

extends that bus into the selectors here

so that'll be the normal run mode but

then when we're in program mode uh

instead of reading data from the bus

we'll be reading data from our dip

switches here and so the way the

programming will work is we'll we'll

switch over to program mode set the

address we want to program here set the

data that we want to put in that address

here and then we want to toggle our

right of course to do that it would be

nice to have a little push button switch

so I've got that

here stick that in there and so this

will just be a little button that we can

push to uh write the data so once we put

the address that we want to write it to

and put the data here push that button

and it'll write it uh to to there uh but

of course again we want to be able to

switch between using this button to

write to memory and the computer being

able to have a control signal that's

going to come from the control logic of

the computer to tell it that we want to

write data into the memory uh so this

this right signal that's going into the

memory now

um has to be switched depending on

whether we're in program mode or not uh

so of course to do that we're going to

uh use another 74

157 which I'll put right here so this

right signal is going to come from the

output of one of

the one of the selectors in this 150 in

the 74 LS 157 um actually should have

maybe connected our power here first get

that underneath there so

power and of course

ground and then again pin 15 of this 74

L1 157 is the essentially the enable

signal so if we want to set that low so

that uh the chip is enabled it's a low

active low uh signal there so that

that's that and so when we're in program

mode we want the this push button to uh

to essentially take the program s or the

right uh signal here low whenever we

push it so we'll connect the uh switch

uh from uh from ground through the

switch and then into the uh the a

input of our 74 LS 157 and so the a

input is is the input that we'll be

using when we're in program mode and

then when we're in run mode um this is

going to be a little bit

different in run mode we want to

essentially take this signal from uh

from the control logic so the control

logic in the computer which we'll get to

in in future videos um at some point

while programs are executing it's going

to say hey I want to write to memory uh

so it'll it'll set this right signal um

but we don't want it to necessarily

write immediately when the right signal

gets set because we want the right

signal to say okay on the next clock

cycle we're going to write to memory but

then we have want to wait for that clock

cycle so really uh we want the right

signal to be a combination of the the

right signal from the control logic as

well as the clock signal um and actually

specifically the rising edge of the

clock so what I'm going to do is

essentially and together using an and

gate uh the clock signal and the control

signal saying uh that we want to write

to memory so I'm going to use a 74 LS 00

um which which actually is not an n gate

it's a nand gate and the reason I want a

nand gate is because this is an active

low so a nand gate is going to say when

the right signal is high and the clock

signal is high then output a zero and

the zero is the thing that that tells

the uh the memory the 74 LS 189's in

this case to actually uh you know take

the data from the bus and write it so

first let me hook up the power for the

74 ls0 the nand gate uh we're just going

to use one of the nand gates on here so

the pin out is pin one and pin two are

the inputs and pin three is the output

so I'm going to hook pin three

here over here to the B input of our

selector so hook that to the B input of

our of our selector so whenever this Nan

gate is outputting a zero and we're in

run mode uh then this selector will will

feed that zero on through to the memory

and we'll we'll end up writing uh

whatever whatever data is coming in so

one of these inputs is going to be the

control signal that's coming from our uh

our control logic which we'll you know

touch on in a in a or we we'll build it

in a in a future video and go into it um

so when that's low then we're not

writing and then if that goes High then

we will be writing something into memory

um so we'll have that low the other

input is going to be from our clock go

ahead and connect this up to our our

clock signal just kind of bring that

bring that back down here and so this is

saying when the clock is high and our

our right signal is high then this goes

low um

which then is passed through so I think

we can go ahead and test this out and

see see what happens so if we power it

up uh so we can see our our clock is

running there and we see of course we

have some random random data here if we

go into write mode uh we can set our

address so if we set the address zero uh

this should write whatever value we have

on our dip switches here so we have all

zeros so we hit

that nothing

happens

H oh of course so we don't we're not

actually selecting here um I neglected

to to connect the actual select pins so

remember these 74

l17s um we want to select whether we're

programming or writing and of course we

have this hooked up you know pin one is

the select pin you can see pin one here

is connected over to this red LED which

goes low when we go into into right mode

we need to bring that that signal down

here so that when we switch to right

mode uh these guys are also selected in

right mode so let me disconnect power

and go ahead and do

that and so that should tie all of our

selects for all four four of the 74 ls7s

the three down here and the one up here

uh to the same switch here and so I

think that should be almost everything

for the ram module so I'll go ahead and

pause here and in the next video we'll

Power It Up and test things out a little

bit more thoroughly