It's been over two months since I thought to myself: "I'll do it!. Hold my beer." So...
I finally had some time to test the prototypes. I built two.
The first one is based on Philips 74F** chips, the second is on Texas Instruments.
That's how it looks:
The results are promising, but there are still some issues.
- Prototype 1 (Philips)
- it works pretty stable after a few minutes, when the chips get a little warmed up
- sees a PQI 1GB 300x PQI card, and, as I thought, does not detect SanDisk 16GB
- sometimes it is, sometimes it is not visible in SpartaDOS, but I managed to divide the card into partitions
- always reads the card data with the BASIC program
- I can load a couple of XEX files (e.g. River Raid, Zybex, a couple of demos) - sometimes the first time, sometimes not. (some of them never - like Gyruss, why?)
- works much better when a fourth decoupling 100nF capacitor is added (so, one per IC)
- Prototype 2 (TI):
- sees both cards, easily detects SanDisk 16GB
- unfortunately, I'm not able to load any program
OK. I'm getting two signals from the motherboard:
- D1xx - U2 (74L138) - pin 14
- B02 - Gated Phase 2 Clock - U18 (74LS08) - pin 11
Do we have to use a buffered signal instead of Phi2 directly from the CPU?
- The U1MB works without any problems when connected to the connector on the board, but it is much harder to read the contents of the CF card. I suspect that the Phi2 track on the PCB is causing interference.
- Probably the noise level is high, we have to think about effective filtering (need to check it with an oscilloscope)
Funny fact: connecting the SDrive to the SIO port makes it easier and more often to detect the card (CTRL+D) (the voltage drops from 5.02 to 4.99V)
What next: XE version - not sure how to do it without U1MB in my 130XE. I think we need an SDX rom image version with the XEL_CF.SYS file for use with i.e Ultimate Cart (or other like SIC!) ...and standalone Loader executable maybe?
Better to write in this thread (after all, it's still an XEL-CF mutation), or set up a new one for this project?
Greetings and all the best in the New Year!