The TMS9129 is essentially a TMS9929 that uses two 64k x 4-bit DRAM chips instead of eight 64k x 1-bit chips.

This is definitely good for reducing board complexity, and the TC-01 used it, but it has become much scarcer and pricier than the TMS9929. There are several ways to make an adapter board:

1. An adapter board with eight 64k x 1-bit chips.

2. An adapter board with a 32K SRAM chip, three latches and a 6-gate inverter chip.

   This is a bit pointless because 1-bit DRAM chips are still widely and cheaply available.

3. An adapter board with two 64k x 4-bit chips and a 6-gate inverter chip.

   A lot of clever thought by Greg of Digicool things went into this.

   This looks the best solution where there are 4-bit DRAM chips already on a host board.

So now I just have to work out how to make the adapter.

I changed the '244 to a '245, and the inverter gate order to make layout easier.

The TC-01 video memory circuit looks like this:

Essentially, we will need to 

• connect an 8-bit buffer so that AD7-0 can drive RD7-0
• DRAM /G pins need their pull-down resistors  R60, R61 removed
• DRAM /G pins need connecting to the new /G signal from the delay line
• DRAM /W pins need connecting to the new /W signal from the delay line

The 9129 socket has no /G pin, so this signal needs carrying on a flying wire.

The buffer and delay gates could sit on a daughter board, with just one flying wire for /G.
Or they could both sit on the motherboard, with a track cut between R/W and /W.

I had a go at editing Greg's fix into the TC-01 video memory circuit diagram.

R60 and R61 tied /G pins to ground via 100R. They can be omitted,

• Fit 64k x 4-bit DRAM chips (4464). The 16k x 4-bit chips (4416) will not work.
• Remove R60 and R61
• Wire the inverters in a delay chain as shown
• Wire the VDP R/W pin to inverter pin 1
• Wire inverter pin 2 to DRAM /G pins
• Wire inverter pin 3 to the buffer /CE
• Wire the 4 or 6 gate delayed signal fed to the DRAM pin R/!W