Shared Projects by KI5NYZ

Teensy-based External Storage

Programming adapter to program M4ROM_TANDY and M4ROM_27256 .

Solid electrical contact with the center pins is made the fact that the receptacle holes in the center of the M4ROM boards are slightly closer together than the pins on the programming adapter.

One pair of the 2.0mm pitch pins on top needs to be cut from a 2x7 header to form the polarity key.

Don’t try to use flush cutters for that, the plastic will shatter and you’ll be left with loose/bare pins.

A hobby knife on a cutting board works better, with a paper towel laid over the header to keep the small part from flying away.

Provides 4 virtual 32K EPROM from a single 128K flash chip, in a Molex 78802 form factor to fit in a Molex 78805 socket.

The pinout at the castellated edge contacts is the non-standard pinout for the TRS-80 / TANDY Models 100, 102, and 200.

NOT for EPSON PX-4, PX-8, TANDY 600, Kyotronic KC-85, Allen-Bradley PLCs, Intermec or Telexon hand terminals, or anything else that has a Molex 78805 socket with a standard pinout. For those, see M4ROM_27256

The chip is written and re-writable using this programming adapter common to both M4ROM_TANDY and M4ROM_27256.

Carrier: http://shpws.me/SGGB

Requires an SOIC-28 test clip for programming.

This is ONLY for TRS-80 Model 100, 102, or 200, because of the non-standard pinout.

For other applications that use the same socket but with a standard pinout (TANDY 600, Epson PX-8, PX-4, etc), see the “Meeprom” version from the same git repo if you want an electrically re-writable module, or just use a plain 27C256 on the standard DIP-28 version of the carrier.

Assembly notes:

For battery holders BT1, BT2, BT3 (NOT BT4!) break the rear walls off before soldering, so that a battery can pass all the way through the holder. Flush-cut everything on the top side as close as possible, and re-flow the cut posts to smooth them into domes. Optionally solder 2 short bits of wire from the two exposed vias to the rear walls of BT4 to mechanically strengthen those walls. Solder a 25mm piece of 0.6mm solid core insulated wire to the GND side of the big yellow capacitor on the REXCPM.

Qwiic adapter wire connections:

BLACK -> new GND pin on the large yellow cap

RED -> pin closest to the cap

BLUE -> center pin

YELLOW -> pin furthest away from the cap