On 06/12/2017 10:23 PM, jim stephens via cctalk wrote: > Things odd about the board. No 1488 / 1489 or any other transmit / > receiver chips. No clock circuit. Was there an appropriate > frequency crystal or clock on the interface to divide to something > for the 1602 uart clock? > > I see transistors randomly across the bottom and "EIA" in the etch, > maybe they got cheap on the RS232 / TTL. The CD4069 cmos chips are > the only things other than the 10 turn pots I see that are other > than TTL and the UART. >
There are a couple of transistors and a diode on the board. Take a look at the SIO board for, say, the Altair 8800. Level translation done with transistors. The trimpot on the board says to me that the clock is most likely a simple RC affair. For low bitrates, that's perfectly adequate. --Chuck
