exxos's Atari, Amiga & retro forum

Reflowing the solder made no difference so I pulled the SRAM daughter board and soldered an SRAM chip (plus the required capacitor) onto the board and it worked first time.

It looks like PCBWay either fitted a faulty chip or it was damaged by the soldering process. *sigh*

Note: NO BODGE WIRES!!!!!!!

HOW IS THIS POSSIBLE?!

Hehe

It's been running GEM for two hours now without issue. Looks like it may be working OK.

stephen_usher wrote: 26 Sep 2021 15:04 Note: NO BODGE WIRES!!!!!!!

HOW IS THIS POSSIBLE?!

Hehe

:bravo:

:cheer: :cheer: :cheer: :cheer:

Tonight I thought I'd had a cunning plan to stop the external floppy drive running all the time and have it only run when the disk was accessed (as the MOTOR-ON signal is always asserted), I'd use the HEAD-LOAD signal, as that should be asserted when data is required and "modern" drives spin up quickly enough.

I was thwarted, however. I didn't notice that it only asserted the HDLD signal when drive A was accessed. Bother!

I'm slowly getting back into designing the hard disk interface emulation again.

I purchased a number of CD4020BE chips as they were advertised as 14 stage ripple counter chips and I need 13 bits of address to sequentially access 8K of SRAM. It wasn't until I started doing a schematic that I discovered that bits 2 and 3 actually don't come out on pins on the chip, only 1,4-14, so they're useless.

Instead I'm going to have to build something out of a 12 bit counter, the CD4040BE and a 74LS112 dual flip-flop (negative edge triggered). Those should be arriving today and I can prototype a circuit on a breadboard over the weekend. I've just got to work out a quick and dirty way of driving LEDs from the outputs so I can see that it's counting correctly. I can then use the signal generator on the new hand-held oscilloscope to clock the counter. I can use the top bit of the counter as an input to the first flip-flop, and the output of that into the second one. The output of this flip-flop can be inverted and passed into the reset, so both chips get reset when the top bit gets set.

Could someone advise me if for a temporary test just sticking an LED + 220 ohm resistor onto a TTL chip pin would work?