On 9/5/2018 2:54 AM, smf wrote: > On 05/09/2018 01:26, Jim Brain wrote: >> It works as designed. /16 mode gives 115200. The T232 used this to >> get 115200 and 230400 (by using the 6551A and double clocking it) >> > Whoever wrote the data sheet seemed to think the /16 mode is only for > working with synchronous TxC (XTAL1) and not an asynchronous with an > external crystal (XTAL1 + XTAL2). > > "On-chip baud rate generator: 15 programmable baud rates from a > standard 1.8432 Mhz external crystal (50 to 19,200 baud)." > > "External 16x clock input for non-standard baud rates (up to 125Kbaud)" > Not sure how you arrived there from that text, but I see no connection. The ACIA supports 15 standard baud rates and 1 non standard one. > > I can't tell what the person who designed the chip was thinking, but > it's rather telling that both commodore and apple don't appear to have > been aware of it when they wrote their drivers. > Most people did not make the connection that 1.8432/16 = 115200. However, I think Commodore and Apple did understand. At the time the devices came out, 115200 was not a bps rate in general use, and line drivers at the time would have struggled to keep up and adhere to the standard. I also seem to recall that EIA relaxed the serial standard at some point to allow the higher speeds to comply with the signalling standard. > > I admit my electronics knowledge is a little poor, so I have no idea > what xtal2 input is and what the chip will do if you put it into a > mode where it would normally be ignored. > XTAL1/2 represent the connections to the Xtal in this diagram. https://en.wikipedia.org/wiki/Pierce_oscillator As you can see, connecting an oscillator to XTAL1 would drive the inverter, but nothing will be connected to XTAL2. The circuit will operate as designed, though. Jim -- Jim Brain brain@jbrain.com www.jbrain.comReceived on 2018-09-05 17:00:05
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