On Wed, Jun 14, 2017 at 6:14 PM, jim stephens via cctalk < cctalk@classiccmp.org> wrote:
> FWIW the send and receive clocks are separate on the 1602 Uart. > That is true of all traditional UARTs. For fancier parts intended for direct connection to microprocessor buses , some have separate clocks, others don't. Some bond options for Z80-SIO have separate clocks for first channel, combined clock for second channel, because the Z80-SIO really had 41 signals, and compromises had to be made to put it in a 40-pin DIP. Separate rx and tx rates was important when using a modem with asymmetric rates, like Bell 202, which was 1200bps in "forward" direction and 75bps in reverse direction. That mostly went away when synchronous modem modulations came into vogue, e.g., Bell 212 and V.22, for 1200 bps full duplex, and most things after that. Even when synchronous modem modulations started having different rates in the opposite directions again, e.g., V.90 and V.92, using a single bit rate on the electrical interface to the modem for both rx and tx had become so ingrained that no one seriously entertained the idea of going back to split rates on that interface. The problem is solved (usually) by flow control.
