There are also a couple of different EPROMS: D27256, with a copyright date of 1984 and D2758 with a copyright date of 1977. Obviously whoever owned these components prior to me was building some interesting embedded systems.
These components coupled with my new EPROM tools were enough for me to bring this vintage processor online. I managed to get the classic blinking LED working as shown on the top trace of my oscilloscope.
|Intel 8035L in Action :]|
The first thing I did was make sure that I could load code onto an EPROM using the MEMprog2 that I ordered. Unfortunately the tools do not support the D2758 EPROMs but they do support the D27256. I decided that I could just tie the upper address bits to ground and it would work fine.
Once I knew that I could successfully load code into program memory I had to find a compiler or assembler (read toolchain) of sorts. I decided to become friendly with the hardware and stick with assembly. The asm48 project looked promising. I have used Windows 7 as my development host for this project since the programming tools are running on that platform. I use VirtualBox to keep a few copies of Windows 7 around for IE web development anyway.
|My test program (3 bytes) and the output of the assembler.|
Early Intel processors combine the address and data bits onto the same lines and use two signals: ALE (Address Latch Enable) and PSEN (Program Store Enable) to signal what state the bus is in. This was done to save costs and keep pin count down. Unfortunately this complicates the connection to an external PROM.
|Various Device Pinouts (EPROM Left, Processor Right, Discrete Logic Behind)|
|Instruction Fetch Waveform|
All of this design work was done mentally. I have drawn it up quickly for your benefit.
|EPROM Interface Sketch|
A keen reader will spot the error in my drawing. CS should be OE.
I wrote a slightly more complex program to toggle the state of the output lines and managed to observe a blinking LED!
|The LED Blink Program|
Perhaps my favorite discovery throughout this process was the fact that this setup uses 135mA at 5V. These days we are concerned about getting into the uA range for low power devices.
I am interested in building a clock using Nixie tubes. I may end up using this processor as the brains behind the operation.