1. AT28C17 EEPROM
By: Ethan Peterson

2. About the AT28C17
Slide 1:
The AT28C17 EEPROM is 2K x 8 Parallel EEPROM chip
The chip being 2K x 8 means that there are 2048 unique addresses in memory and each one contains 8 bits or 1 byte of data
The chip comes in a 28 pin DIP (Dual Inline Package) and is made by Atmel
The datasheet dates back to 1998 so from what I understand the AT28C17 is very old

3. HOW to UsE the AT28C17 Slide 2:
On the board is the pinout diagram of the AT28C17
When reading or writing to the chip you must select a memory address. The address value is placed on the 11 address pins A0 to A10. A high value representing a one and a low value representing a 0. With all the address pins set high or low an 11 bit value is formed that serves as the memory address. It is these 11 pins that allow you to navigate to over 2000 unique memory addresses on the chip.
Once you have selected an address you must use Input Output pins to either read the output from that address or write to it. There are 8 I/O pins matching the 8 bits available at each memory address.
The process of reading writing is quite unique from anything else we have used in the ACES program so far as you simply place your data in the form of high or low values along 8 pins as opposed to something like a shift register where there was data pin and a clock pin to clock the data into the register one bit at a time.
The other key pins to take note are OE, CE, WE and RDY/BUSY
OE stands for output enable
CE stands for chip enable
WE stands for write enable
A combination of these three pins in high and low states allows you to perform device operations such as reading and writing.
For example, to read the data from a specified address on the chip you must set CE and OE low and write enable high which asserts the data at that address on the IO pins.
This makes sense as the line over the WE OE and CE indicates they are only enabled when in a low state

4. What ROLE Does the AT28C17 Have in the Chump?
Slide 3:
The AT28C17 performs two functions within the CHUMP computer.
It acts as the program ROM storing the 8 bit machine code instructions the CHUMP requires
Another AT28C17 acts as the Control ROM which is indexed by op codes. If you read from the address of an op code the 8 bits asserted on the outputs of the EEPROM control the other various chips in the computer to perform the task you expect. For example, if you navigate to address 0 that is the op code for load so the output pins would assert a value that would control the other chips to do the load command.

5. Questions?