Rev I 1802 Membership Card

[rev I CPU]

[rev J assembled]


Page last updated Aug 25 2017, one fix May 16 2018, one fix Jan 22 2020

This is the support page for the Rev I 1802 Membership Card, OUT of distribution as of July 1 2017. This page contains MANY Web links with support and use information. The Rev I front panel has new features over Rev H2. This page will show prior versions of photos and documents until Rev I versions become available. Links to order and for more information are below.

The photo on the left is of the assembled Rev I CPU board, by Herb Johnson; Rev I is slightly different. The photo on the right is an assembled and stacked Rev J 1802 Membership Card set - looks the same as the Rev I - by Herb Johnson.

"For those just tuning in, the Membership Card is a reproduction of the original Popular Electronics COSMAC Elf computer, but shrunk to fit in an Altoids tin! It works the same, and runs the same software." - Lee Hart, developer.

Prices, ordering, contact

How to order: Order the Membership Card from the 1802 Membership Card home Web page. The page has links to current and previous 1802 Membership Card version pages. It also has links to 1802 history, testing, hardware, software, and more.


Product and documents
Rev I features and options
Initial testing and programming
Rev I detailed description
Engineering Data
Hardware and software and notes about them
Errors and corrections
Chronology of Membership Card products & support Web pages
Prices, ordering, contact

Pages edited by Herb Johnson, (c) 2017 Herb Johnson, except for content created by Lee Hart and others. To report errors on this page, contact Herb at, an email address is on that page. - Herb Johnson

Product and documents

[parts kit] [Rev I front panel]

Documentation, rev I: The Rev I manual is a .PDF file at this link. dated April 4 2017.
Here's the link to the Rev I schematic dated Feb 24 2017.

On the left is a Rev F kit parts from Jan 2014; the current parts kit looks very much the same. On the right, is an assembled Rev I front panel atop a CPU, by Lee Hart.

Rev I features and options

Small size, ordinary components, assembly manual for hands-on building. The front panel and CPU boards stack to fit in an Altoids tin. The front panel cover board (optional) fits over the Altoids lid. Only common readily-available electronic parts are used (except the 1802) and are part of the kit. All thru-hole parts, for easy hand assembly. Assembly manual guides construction, part by part, with testing and debug information.

Run without a PC. No PC, external hardware, or any onboard program, are required for use. Front-panel runs, halt, loads by toggling switches. LED binary display. These are same features as the classic COSMAC ELF; plus RAM, ROM and I/O options as described here.

stable clock frequency with ceramic resonator AND variable clock with trimpot.

Low-power standby, nonvolitile RAM: Seperating the CPU board from the Front Panel, or disconnecing the power connector, will put the CPU board into a "standby state", program halted and RAM contents saved by the supercapacitor.

RAM and ROM on one CPU board The kit comes with .6-inch wide RAM chip. A ROM can be installed instead and a .3-inch wide RAM chip can be installed under it, to support a ROM/RAM based monitor. A bypass capacitor must also be added.

Load/run and data transfer via "parallel port". The front-panel has a DB-25 connector for 8-bit data in and out. The DB-25 arrangment matches the traditional "PC parallel port". Old-school PC's under MS-DOS can run programs in QBASIC to download and run Membership Card programs; the Windows OS limits that capability and modern Windows computers lack the parallel port. So some M/S card owners have built microcontrollers to operate the Membership Card. See this Note about use of the parallel port by old PC's, with links to examples of use of microcontrollers. Rev H, H2 has more ways to set up the DB-25 connector for 8-bit operation.

serial interface operation via EF3 and Q with an RS-232 interface on one connector, a TTL or 3.3V serial interface on another. A two-color LED shows serial activity on Q and EF3. Serial operation requires a ROM or program to support a "software UART" and to interact with the serial user. The TTL connector is also the +5V power connector and can be compatible with some USB-to-serial adapter cables.

optional ROM monitor and serial connector kit: A "kit" with serial connector, IDIOT monitor ROM and RAM and specific instructions, is described on this linked Web page. A more general and technically detailed discussion of the serial interface and operation of a ROM monitor is on this linked Web page. Other monitors or programs can be run from your own ROM or from RAM, see the software notes below and the Rev I manual. Serial features were discussed in more detail on the Rev G support page.

How To order

To order: Refer to the Membership Card home page for the current ordering status. An email address and Web link takes you to developer Lee Hart for ordering and contact.

Your initial tests and programs

The kit manual has test programs and debug information. Also, see this document on Testing the 1802 Membership Card with small toggle-in programs. Basic operations of the front panel are described. There's more links about testing and use, under "features" on this Web page. Other links are to testing hardware Web pages and testing software Web pages are on listed on the home Web page. - Herb Johnson

Rev I detailed description

The Rev I Membership card set, consists of a CPU board stacked on a Front Panel board. You can buy the boards, or a kit with boards and parts. And, you can buy a Cover Board, a circuit board to cover the switches and lights of the Front Panel card. These are all sized to fit an Altoids tin box.

[Rev I CPU]

1. Membership Card CPU Rev I board:

Rev I CPU bare board on left. Edge-on assembled rev I on right.

- 1802 microprocessor (option for 1804/5/6 which have no load mode).
- .6-inch 24-pin socket for 2K to 32K byte-wide RAM or ROM
- also .3-inch 24-pin socket under ROM/RAM for narrow SRAM.  
[edge view] - supercapacitor to maintain RAM contents with power disconnected or /ON asserted - one 8-bit output port (OUT4 default, or you can jumper-select others) - output port multiplexed to four DB-25 pins (PC parallel port) - OR all 8 bits out to eight DB-25 pins (jumper selected) - one 8-bit input port (INP4 default or you can solder-jumper select others) - HI/LO jumper select on board ROM/RAM for high or low 32K address space - optional +5 volt power input at DB-25 pin 18 w/diode protection (jumper selected) - Rev H forward, adds diode to /CLEAR for power-on clear - ceramic resonator for stable clock, and adjustable with trimpot - the usual 1802 I/O bits (Q, EF1-EF4, INT, etc.) - all I/O and power brought out to a 30-pin header - size: 3.5" x 2.125" - power: 3-6vdc at 1ma (depends on clock speed, several mA for ROM and RAM memory chips)

[Rev H front panel]

2. Membership Card Rev I Front Panel:

Rev I front panel bare board on left.

- plugs onto the 30-pin connector of the Membership Card 
- no PC, external hardware, or any onboard program, are required for front-panel use.
- run, halt, load control by toggling switches, LED byte display
- provides the Elf front panel interface and "classic PC" DB-25 parallel interface, 
- optional serial interface with LED activity, software bit-driven from EF3 and Q.
-  serial receive, transmit support TTL or RS-232 voltages, or some USB-to-serial adapters
- 8 data output LEDs (memory reads and OUT4)
- 1 Q output LED
- 8 data input toggle switches (memory writes and INP4)
- read/write memory, run/clear, run/load toggle switches
- 1 input and EF4 pushbutton to load front-panel switch data
- "stand alone" memory read, write, program load, and run operations
- size: 3.5" x 2.125"
- power: adds about 3ma for each red LED lit, less with other LED's
(assembled Rev G photo by Lee Hart)

DB-25 PC parallel port connector on Front Panel:
- has all I/O and control signals to classic PC parallel port (8 bits in, 4 out)
- can control run/halt/load front-panel operations
- jumpers to bring out all 8 bits and bring in +5 on DB-25

6-pin serial/power connector
- RX/TX and +5 volts compatible with some USB-to-serial adapters
- adds "idle" signal, could be connected to serial (TTL level) RTS line or toggle switch.

[panel cover]

3. Membership Card Cover Board:

Cover board on left as part of Rev I built kit. Built by Lee Hart.

The Membership Card Cover Board is a PC board to cover the Altoids lid and mounts on the Front Panel board. The board has holes for the switches and lights, power/serial connector, and DB-25 connector. There's silkscreened labels and a tinned copper shield on the back. Cut a large rough rectangular hole in the Altoids box, and solder or epoxy this board to the top to provide a neat finished front panel.

How to Order

Refer to the Membership Card home page for the current ordering status. An email address and Web link takes you to developer Lee Hart for ordering and contact.

Engineering & Change Data

For details of previous revisions, look for the Web pages for those revisions. The text below is edited from a summary by Lee Hart, Jan 17 2017. - Herb Johnson

Rev I CPU board: No functional changes from Rev H2. A few parts and traces were moved here and there, to increase spacing in places where there were reports of solder shorts or tight fits.

Rev I front-panel board: A diode D15 was added across C8, to keep C8 from charging positive and creating an "active" condition on /EF3 when serial connections are "idle". Read this Tech note for details. The diode is soldered on the back of the board, as described in the most-current Rev I manual on this Web page.

Rev J change to Q LED: The Rev J front panel board, changed how the Q LED is driven, to make serial activity more visible. Read notes on the Rev J support page for details, see if you want to modify your Rev I. - Aug 2017

Changes to serial connections: TTL and RS-232 seperated

Rev I Front Panel board power/serial connections: I replaced the previous-rev's Front Panel 4-pin power connector P4, with a 6-pin power & serial connector as described below. P4 and the DB-25 connector J2, support different "active" voltages for serial, as detailed below. The silkscreen for Q4 is wrong. See the note on page 10 of the Rev I manual.

On P4: P4 is now 6 pins and has the same pinouts as the Sparkfun model 9718 USB-to-TTL serial cable, currently with FTDI FT232RQ chip; and other FTDI-232 clones. The TTL-level serial input and output lines are routed to the extra two pins. People should be able to plug that USB right into a PC, run a terminal program (Hyperterm or whatever) for both power and serial I/O. [Attach your USB-to-serial adapter, for both power and serial connections as described below.]

The old P4 had 4 signals; +V, RUN, LED, and GND. RUN had to be high to enable the 1802. LED had to be grounded to enable the LEDs. I combined these two pins into one, called /ON. It is controlled by RTS from the Sparkfun cable (or a jumper or switch if you're using an external power supply).

name    P4 pin    function
----    ------    --------
-    	1    common (ground)
    	2    key (no pin)
+    	3    power - +3 to +5 volts DC
RX    	4    receive serial data (TTL level, idle high, active low)
TX    	5    transmit serial data (TTL level, idle high, active low)
/ON    	6    low - enables clock, runs 1802, and enables the LEDs
        	high (or open) - stops clock, resets 1802, disables LEDs

The old LED signal is renamed /ON. A new transistor Q6 inverts the /ON signal to provide the high RUN signal to the 1802MC. If left open, it floats to the "off" state. You could, for example tie it to ground with a switch as your on/standby switch. (In standby, power is minimized and the supercapacitor is maintaining memory).

The Windows Hyperterminal program happens to set RTS high when not "connected", and sets RTS low when "connected". Thus the connect=run, and disconnect=standby.

On J2: The RS-232 level TXD and RXD signals are still on the 25-pin D-connector (J2), so you can still connect it to classic RS-232 terminals or old-school computer serial ports. These lines are current limited with series resistors, to reduce power consumption. Also: they will work with USB-serial adapters with 3.3v levels. or with 5V levels.

To make room for the new parts, I eliminated the TTL and non-inverted options from the DB25 connector. It is *always* RS-232, and *always* inverted. Idle negative (low, voltage below 0 volts), and active positive (high). It works as if you connected the 1802 Q and EF3 pins to the RS-232 lines with a MAX232 interface chip, or 1488 or 1489 IC - which are all inverters.

Thus P4 is always TTL level "true" data, and J2 is always RS-232 "inverted" data.- Lee Hart

Inverting /EF3 serial input: If you need to invert the serial TTL input on the Rev I or J card, here's a means described by Al Williams. He provided this description, in his notes about use of the Spare Time Gizmo's version of the "ELF2K" ROM monitor and utility. "The solution I used, was to clip R2 off the circuit board completely. Then I wired the left pad of R2 (which connects to P4) to the banded end of D13. This uses Q5 as an inverter. This is equivalent to jumpering [the TTL serial input pin] to pin 20 of the DB25 connector." - Al Williams, July 2017

Al's notes on using Elf2K with Rev I are in his files on the cosmacelf Yahoo Web site. You may have to be a member to obtain the file.

Other Engineering notes:

"Excessive detail" on RS-232 levels on J2. "RXD must be (-1v to -12v) to be "low", (+3v to +12v) > to be "high". (The actual RXD threshold is about +1v.) TXD will be (RXDlow + 0.6v) when "low", and (VDD - 0.6v) when "high".For example, if the 1802MC is running on 5v, then TXDhigh = 5-0.6 = 4.4v. If RXD is -5v, then TXDlow = -5+0.6 = -4.4v." - Lee Hart, Jan 22 2016.

Use of /ON via RS-232 signal RTS: RTS is idle HIGH; that's the *off* or standby state for the clock, 1802, and LEDs. RTS goes low (active) when you tell your PC terminal program to "dial" or "connect". That pulls /ON low, the clock starts, the 1802 comes out of reset and runs, and the Front Panel LEDs are enabled. To switch it off, tell your terminal program to "disconnect" or "hang up". - Lee Hart, Jan 22 2016. Note: confirm your terminal program or USB/serial adapter performs these functions with RTS, or connect a switch to ground for manual operation.

Notes on SRAM narrow-RAM bypass capacitor C6 Comment by Lee Hart apr 2015: "If you BUY these capacitors, be sure to get them with X7R dielectric; not Zxx or Yxx series dielectrics. You need a good fast capacitor to properly bypass those dammed-fast 0.3" RAMs. They have really nasty power supply current spikes." The Rev H manual describes the part as "C6: 0.1uF X7R axial lead ceramic capacitor (Mallory P20R104K5; Jameco 536542)". It's "axial", a cylinder with leads at either end.

CMOS .3-inch RAM: Many 300 mill SRAMs are not CMOS, not low power. Read this linked Web page about current-consumption tests for a variety of brands, models and speeds of .3-wide RAM. Here's another link to some earlier engineering notes about power consumption, program retention, current consumption of LED's by color. There's also more information in the docs of previous 1802 M/S card versions.

Recent versions use resistor biased transistors for the serial interface or other functions. A Tech Note about transistors with internal resistors, used on the M/S card serial I/O. Here's the data sheet for the FJN3307 NPN and Here's the data sheet for the FJN4303 PNP

Hardware and software and notes about them

This Web site has dozens of Web pages about hardware, software, operation and upgrades and debugging of the Membership Card. Please, please look at the Home Page of the 1802 Membership Card for links to those notes. Collections of hardware note Web links and software note Web links are on these linked pages.

Aug 2017: Lee Hart and Chuck Yakym now provide a BASIC, a Tiny BASIC, and a ROM monitor; as binary images for ROMS or binary download. See his 1802 M/S card sales page under "BASIC for the 1802". Details are in the ZIP files and on his site. There may be copies in "The Eagle" folder by Chuck, on the cosmacelf Yahoo Web site.

June 2017: Many people use a USB to serial adapter to operate the 1802 Membership Card serial port. Over time, it's been discovered that these adapters introduce hardware buffering of characters sent and recieved. This buffering interferes with timing delays caused by 1802 software, and delays deliberately added by "terminal" programs on the PC in use. Here's a Tech Note which is from discussion of these USB serial issues, from posts in the cosmacelf Yahoo discussion group. - Herb Johnson

Jan 2017: Lee Hart says "So far, I have tested [the 1802 Membership Card] with the following ROM monitor programs:
- Herb Johnson's IDIOT monitor
Chuck Yakym's monitor + Tiny BASIC at cosmacelf Yahoo
Spare Time Gizmo's Elf2K EPROM

Lee Hart in Dec 2015, looked at some TTL to USB and DB-9 RS-232 to USB adapters. Others in 2017 have used additional adapters with their 1802-based computers. Here's they have to say, under "Useful USB serial adapters". Further notes about the art of bit-serial on the 1802 M/S card is on this how-to Web page.

In June 2014, David Kriest assembled a Rev G CPU card as a stop-motion video. See the video on Youtube as "MC Revg" by "Corecoder" for June 13 2014.

To order: Refer to the Membership Card home page for the current ordering status. An email address and Web link takes you to developer Lee Hart for ordering and contact.

Errors and corrections

Jan 30 2017: The silkscreen for Q4 is wrong. See the note on page 10 of the Rev I manual.

History of 1802 Membership Card production.

The 1802 Membership card has had many design changes, to improve operation, provide more user options, or to correct problems. Review previous version's support Web pages for discussions of those changes, or for guidance to use the current version. Consider buying a new-version CPU or front-panel card versus modifying your version. There's often links to notes about such "mods" on the version-pages.

July 1 2017: Rev J CPU and Front-panel is in production and distribution.

Apr 1 2017: Rev I Front Panel is in production. The H2 CPU was still in distribution until supplies exhausted; then Rev I CPU boards were distributed. This Web page is the Rev I support Web page.

July 2016: Rev H2 Front Panel in production with Rev H2 CPU. A 3.3K resistor R2 was added in series with the RS-232 input; as a change to Rev H.

June 2015: Rev H2 CPU in production with Rev H F/P. The Rev H CPU /A15 address inverter NPN transistor Q1 replaced with 5LN01SP N-channel MOSFET and 5LP01SP P-channel MOSFET to produce the /A15 signal (chip-select for memory at 32-64k). Rev H2 CPU also has a normal 4-pin header for [HI/LO] memory address selection, located on the top of the board.

Apr 2015: Rev H in production. Changes to CPU: /A15 FET Q1 changed to transistor to improve rise-time at reduced current. /CLEAR diode, to reset with or without front panel. Rev H front panel: 5-pin jumper for serial input, to invert or non-invert. Some Rev H CPU boards were sold with Rev G kits.

Check the 1802 M/S Card home page, for links to ALL previous version Web pages. Further details of production and change history are on a history of production Web page.

30 years ago, Lee developed an 1802 single board computer called BASYS. Look at the BASYS manual for hardware interface suggestions for the Membership Card.

How to Order

Refer to the Membership Card home page for the current ordering status. An email address and Web link takes you to developer Lee Hart for ordering and contact.

This page and edited content is copyright Herb Johnson (c) 2017. Contact Herb at, an email address is available on that page..