OK, I think it's time to start this topic. I almost have everything I need I think. First I want to copy and paste some important information from another thread () just to consolidate it here:
Tursi, on 05 Jan 2017 - 04:21 AM, said:
ROM Select and GROM Select should be enough. The problem with the Navarone Widget is it did NOT cut GROM Select. For some reason for the GROMs it cut the -5v, which the UberGROM doesn't use.
Sinphaltimus, on 09 Jan 2017 - 8:28 PM, said:
ROM Select? Maybe +5 and the GROM Select?
Tursi - "GS* (GROM Select) and ROMG* (ROM Gate).
Switching power isn't recommended, although you would need it if you get too many carts on there. (I have no idea how many too many is). The problem is that when you activate power to a chip, it likely won't be a clean transition and can cause the chip to malfunction."
Name I/O Use
- ---- --- -----------
1 RESET < Resets the system (active high)
2 GND Signal ground
3 D7 <> Data bus, bit 7 (least significant)
4 CRUCLK* > Inversion of TMS9900 CRUCLOCK pin
5 D6 <>
6 CRUIN < CRU input to TMS9900
7 D5 <>
8 A15 > Address bus, bit 15 / also CRU output bit
9 D4 <>
10 A13 >
11 D3 <>
12 A12 >
13 D2 <>
14 A11 >
15 D1 <>
16 A10 >
17 D0 <> Data bus, bit 0 (most significant)
18 A9 >
19 VCC +5 Volts power supply
20 A8 >
21 GS* > Grom select. Active low is addr in >9800-9FFF
22 A7 >
23 A14 > Address bus, bit 14. Select mode: low=data / high=addr
24 A3 >
25 DBIN > Active high = read memory
26 A6 >
27 GRC > GROM clock: color burst of VDP 9918A
28 A5 >
29 VDD -5 Volts power supply
30 A4 >
31 GR < Active high = GROM ready
32 WE* > Active low = write enable (derived from TMS9900 WE*)
34 ROMG* > Active low if addr in >6000-7FFF
Here's the idea I'm going with.
I'm going to mount an edge connector to a large board along with 4 cartridge ports. With 4 carts installed, you should just barely be able to slide a piece of paper between carts.
Lined up along one side will be an AV switch box with 4 buttons. The input AV output jacks will be shorted to complete the circuit. Basically, connect RCA plugs with their individual wires soldered together. This way I can splice the GS* (GROM Select) to left audio in and the ROMG* (ROM Gate) to right audio in per 4 inputs. Since I still have the ability to cut more lines (the video jack and the S-Video jack) per button, is there another cut you'd recommend? Like maybe the + &/or -5v? Or no?
The finished project will work by simply pressing the 1 button for cart 1 or 2 for cart 2 etc...
I'm not at all concerned with the ability to switch carts with the console powered on although it would be nice. That's why I'm wondering about cutting additional lines. Shutting the console off to switch is fine however. I'm really just looking to cut down the wear and tear on the cart port. The 4 cart expander will be connected to the console via cart expander cable. It's a personal project to solve a personal need at low cost. I will document it all with photos and text as I make progress sharing the experience and hopefully have a fully functional 4 port cart expander by the end. Remaining hopeful I will be able to start this coming weekend.
This is the exact switch box I plan to use.
Edited by Sinphaltimus, Thu Jan 19, 2017 4:52 AM.