You may look for 27C1000 (NOT 010 nor 1001) EEPROMs, but they are likely to be 200ns ones, so on the very border line of the acceptable latency for a stock 8MHz ST. They are 32 pins, but the "excessive" pins can be tied together and hooked to VCC (except \OE which should be tied to GND). You may als...

It's pretty common in C... Set bit 3 (0 based index, so bit 3 is 4th bit): a|=(1<<3) Clear bit 3: a&=~(1<<3) << - shift left | - bitwise OR & - bitwise AND ~ - bitwise NOT Unfortunately Spectrum BASIC doesn't have bitwise operators, it only has logical ones :( I'm unsure if in HiSoft BASIC it is any...

So exactly opposite to my issue, but somehow expected - I was using a true DD drive in Atari and a DD formatted HD diskette together with a HD drive in PC. It is not as bad as with 5,25" disks, but HD drives dislike DD disks and opposite way around too. It works when formatted, saved and read in the...

Was it a true DD floppy or a HD floppy formatted to 720kB? With the latter ones, I had the same problem.

Actually, there existed a 1Mbit non-JEDEC compatible EPROMs, which had the same A16 and /OE pin locations as MASK-ROMs, these were 27C1000 and 27C301. /CE pin location (22) is the same with all 27C1001/010/1000/301 and the MASK-ROM (you are showing pin numbers for 28 pin 256kb MASK-ROM)... or maybe ...

These are not even resistors, but just a fancy jumper wires... apparently someone moved them from one position to another from the top (without removing the board from bottom case).

Yet another C070789-001 REV .D:

I have recently found a very interesting chip called Si5351A. It is a 3 channel clock generator (8kHz - 160MHz). All 3 clocks can be phase locked. Chip is programmable by the I2C bus. It is available as an breakout board from Adafruit, or from Aliexpress. Have anyone considered using it for an ST bo...

As far As I remember it needs +/-12V solely for UART (RS232/MIDI), and of course +12V also for floppy. Good thing is, a custom PSU may have two plugs - one for ST and one for SF floppy.

Good replacement is also an Astec AA21430 (it was used in CISCO 1800 series routers). Connector is a regular DIN-7F. Same cable fits also SF3x4 floppy drives (despite they use DIN-5 and don't have -12V line).