Port B uses the CLOCK2 signal from the enhanced bus. Port A is wired to always use the CLOCK signal from the standard bus. Port A is the primary port, wired to the RX and TX pins on the standard RC2014 bus, while Port B is wired to RXB and TXB on the enhanced bus. The Dual Serial SIO/2 module supports two serial ports. Each clock can be jumper-selected to a variety of rates, including divide-downs of the fast 7.3728MHz clock corresponding to standard baud rates down to 4800. The CLOCK2 signal on pin 21 of the enhanced bus is available for other uses. The CLOCK signal on pin 21 of the standard bus is used by the processor and related peripherals. The Dual Clock module generates two clocks.
MIXSCOPE MAC OS X HOW TO
This mod shows how to change the baud rate for one common RC2014 configuration, using the Dual Serial SIO/2 with the Dual Clock module. Both boards simply feed the bus clock to the chip to generate a fixed baud rate of 115200 bps.
Unfortunately neither the MC68B50 ACIA used on the original RC2014 Serial I/O module nor the Z80 SIO used on the current Dual Serial SIO/2 module has an internal baud rate generator.
At least part of the problem seems to be that the standard baud rate of 115200 bps is way too fast for the 7.3728MHz Z80 processor to handle. Many users of the RC2014 retro computer have had difficulty getting XMODEM file transfers to work.
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