Electronic Systems TRS-80 Serial I/O Board?

Noel Chiappa jnc at mercury.lcs.mit.edu
Wed Jun 14 09:44:47 CDT 2017

    > From: Brent Hilpert

    >> The trimpot on the board says to me that the clock is most likely a
    >> simple RC affair.

    > There's a 7493 (4-bit counter) on the board as well, which looks to
    > have connections to the dip switches beside it, in all likelihood the
    > baud rate divider and rate selection

Yes; but the trim pot is also there because one has to set the basic clock to
one of two values, depending on whether one wants the 150/.../2400
selections, or the 110/etc selections; one has to set it to 26 usec for the
former, and 35.5 usec for the latter.

So drift would have been an issue, but not initial component values...


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