Re: Mar1e gets (some) address LEDs #Homebrew #Electronics

John
 

Hi All,

Earlier I wrote "and I've added a 4-way DIP switch. The left-most switch holds the active-low MW pin of the battery-backed RAM chip high for switching off and on, that way the RAM contents don't get corrupted."

I was wrong (forgotten already!) The left-most switch was used to pull the active-low chip select high, it was nothing to do with write enable. While running the chip select was held low, then I took it high for power down. I've disconnected the switch now and so far I haven't had a problem with memory loss. 

I've made a new back apron for Mar1e today, with a 9-way D socket for serial and a 25-way D socket for parallel and analog interfaces, none of which I've added yet. I'm eyeing-up the remaining space on the board for a 74HCT373, a MAX232 (no 1488/1489 for me as I don't want to have to add two more power rails) and whatever else I can fit. I think the two D sockets might be too close together, depending on the with of the covers. I've found a Psion Organiser XP (two line display) and two comms links, both with 25-way D connectors. Somewhere I have one where I swapped the connector for 9-way, but I haven't found it. Somewhere, too, I have a Psion LZ64 and an original LZ which I made into a 64 by adding more memory. Four lines would be good.

John

On Thu, 11 Apr 2019 at 17:52, David Madole <david@...> wrote:
John wrote:
> I fancy building an AFSK oscillator too, 1275/1445Hz, so it can talk
> acoustically to an RTTY app on my Android tablet at 50bps. I love that
> warbling sound!

Try just putting a speaker on Q and doing the tones in software.

David




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