Wichit Sirichote 1802 Microprocessor

The 1802 Tester

2020-12-10 I have been selling 1802 CPU on my web store from the beginning and occasionally on eBay. One of the advantages I've had has been that I can know with confidence if the CPU is working before I sell one. I test every CPU sold before it leaves here. This is how I do that.


I am the lucky owner of an 1802 CPU Tester. It is designed and manufactured by Molnar Kalman in Hungary.

You can get them here at CPUShack. RCA 1802 CPU Tester You can get the PDF manual at this link RCA1802_testboard_manual.pdf * Update * You can also get them directly from Molnar whom accepts paypal. It is slow shipping from Hungary but worth the wait.

You can get the schematic RCA_CDP180x_tester-v1_0_sch.pdf You can find Molnar's email address in the PDF manual.

When I purchased mine a few years ago I purchased on eBay. They are selling for $US 90 there using paypal. I highly recommend these 1802 CPU Tester, I have been using it for several years.

I mounted mine with brass standoffs onto a small piece of acrylic with rubber bumpers mounted on the bottom. You should mount it on something you can drag around your work bench safely with power on.

If you are looking to purchase some Harris 1802 CPU, please purchase CDP1802ACE Harris 1802 CPU H9640 NEW TESTED at Hardware for Hackers.

The CDP1802 test board is intended to test the working condition of RCA CDP1802 COSMAC and compatible CPUs.
The board consists of the base components of RCA CDP1802 test system:

  • 40-pin ZIF socket – for CDP1802 CPU – provides easy replacement of the CPUs.
  • 2.4MHz crystal oscillator connected to CPU for generating system clock.
  • Address latch for bits A15-A8 of address BUS

A 2716 2KB EPROM holds the test program. This program supports 4 push buttons as inputs, and 8 LEDs, as output devices. It also provides basic and special feature test routines.
The board requires a single +5V power supply (200mA) provided through a mini-USB connector.
There is a power switch and power indicator LED in the upper left corner of the test board.
Address, data, system control and power lines are attached to the three 16-pin expansion headers, so that the board may be used for other projects.

  1. Mini-USB 5V power supply connector: The board consumes around 200mA current so a computer USB connector or cell phone charger that can provide at least 300mA may be used as power source.
  2. Switch: Power supply can be turned on and off by the sliding switch at the bottom right corner.
  3. Green LED: next to the power switch, indicates the power level of 5V.
  4. Reset Button: The board contains a Power-Up reset circuit, but can be reset manually by pressing Reset button.
  5. 40-pin ZIF socket: for the CDP1802 CPU. Ensure proper CPU orientation!!! The pin-1 is at upper-right corner, next to the release lever of the socket.
  6. Red LED: Labeled Q, indicates the status of the CPU output Q.
  7. Eight output LEDs: – Show simple animations, flashes – indicate that the CPU is working.
  8. Four push buttons: Used for testing inputs and changing animation sequences.

Before changing the CPU in the ZIF socket, make sure the power is off. All power indicator LEDs should be off!
Place the CPU into the socket (socket lever should be in the UP position). Ensure proper orientation to prevent damage to the test board and CPU! Pin 1 must be at the upper-right corner, next to the release lever of the ZIF socket. Then lock the socket by moving the lever down into the lock position.
Connect the power through the USB connector and switch the power switch to ON.
The power indicator LED should be illuminated.
If the CPU is in working condition the 8 output LEDs should be flashing (1s on/1s off pattern).
At this point the CPU can be considered WORKING. Congrats!

Base Function Test
When you press any of the four push buttons (SW1 – 4) the output LEDs copy the state of the buttons, duplicated in the low and high nibbles.
Press and Releasing the buttons causes one of the four different animation sequences to start, corresponding to the button released last.
During the animations selected by SW2 or SW3 the Q LED blinks periodically.
These test routines use the base instructions and features of CDP1802 CPU.

Special Feature Test
These test routines check if the inserted CPU can execute the enhanced instructions of CDP1804, 1805 and 1806 CPUs, then check the timer function and the internal RAM.
To activate the special feature test SW1 and SW4 should be pressed together and held for 3 seconds.
First the enhanced instruction capability is tested and the result shown on LED D1& D2.
Then the timer functionality is tested. It takes about 1s and the Q LED blinks rapidly during the test. The result is displayed on LED D3 & D7.
Finally the internal RAM of CDP1805 is tested. The result is shown on LED D4 & D8.

  • D1 – CPU type 1802
  • D2 – CPU type 1804, 1805 or 1806
  • D3 – Timer OK
  • D4 – RAM OK
  • D7 – Timer failure
  • D8 – RAM failure

2019-02-19 I finally received the board and I am very happy! It is so much easier to work with than the Membership Card. You can learn a lot more about the CDP1802 Microprocessor Kit from Wichit Sirichote.



R1      EQU     1
start   ORG     8000H
L0:     LDI     10H
        PHI     R1
L1:     DEC     R1
        GHI     R1
        BNZ     L1
        BQ      start
        BR      L0

   0001                 R1      EQU     1
   8000                 start   ORG     8000H
   8000   7a                    REQ
   8001   f8 10         L0:     LDI     10H
   8003   b1                    PHI     R1
   8004   21            L1:     DEC     R1
   8005   91                    GHI     R1
   8006   3a 04                 BNZ     L1
   8008   31 00                 BQ      start
   800a   7b                    SEQ
   800b   30 01                 BR      L0
   800d                         END

8001  L0            8004  L1            0001  R1            8000  start


You can get a18 from Herb Johnson version of a18 It compiles fine on Ubuntu 18.02.

gcc -I. -o a18 a18.c a18util.c a18eval.c
len@spectral:~/Cosmac_Elf/a18$ ./a18 blinkQ.asm -l blinkQ.list -o blinkQ.hex
1802/1805A Cross-Assembler (Portable) Ver 2.5+
Copyright (c) 1985 William C. Colley, III
fixes for LCC/Windows by HRJ Aug 2010

No Errors

The best way to load programs is to use the LOAD key, which accepts input from the serial terminal.
You will need to set a character delay. I normally use Linux, so it's minicom, which is easy you enter the terminal settings menu and add (example) 4ms delay.
That was enough to solve my problems, your situation may be different depending on uart, cables, etc.


Once you've set the right character delay within your terminal program paste the hex code into the terminal.


If the paste worked you will see "0 error…" but this is a misnomer as well because I've had it drop hex characters with "0 errors" but loaded garbled code. If you use a character delay you will be fine, however.

2021-05-20 I haven't done much with any of my 1802 projects lately. I have been selling a lot of 1802 CPU. I have both the Harris variant and now even genuine RCA chips. That is why I was making an update today actually. I always really only wanted the Harris chips. They were manufactured recently and are very high quality being produced by the most modern manufacturing processes. I love the RCA CDP1802 but all of the chips I have are very old. I can't be sure but some of them appear to be "pulls" which I have not been able to sell in good faith.


It turns out that when you order from a firm labeled "HARBLL Automotive performance chip Store" from AliExpress they advertise Harris chips. I ordered a few hundred of them because I have been selling them at my store Hardware for Hackers and on eBay. I was running low on Harris chips so I was being diligent and trying to keep them in stock because people are still using the CDP1802ACE in their projects and a lot of people are exploring the world of assembly language thanks to the CDP1802 cpu. I guess it has something to do with the history.

Anyway avoid "HARBLL Automotive performance chip Store" from AliExpress at all costs they are liars and thieves.

Oh any way, I have a plethora of genuine RCA CDP1802ACE chips for sale. Some of the markings are somewhat faded but most are quite legible. I examined each one with a jewelers loupe and tested them in my cool 1802 tester so they are guaranteed not to be DOA. This is turning into an advertisement but if you want to get some the link is Genuine RCA CDP1802ACE CPU NEW TESTED I guess they are like 40+ years old depending on the batch. How long since RCA actually stopped manufacturing the CDP1802? I suspect it is a very long time.