> The 8250, 6551, Amiga serial port, etc do not have FIFOs and so generate one > interrupt per byte. The CPU has to respond to the interrupt and retrieve the > incoming byte before the next byte has arrived. At 9600 baud, that needs to > happen within 1ms. At 115,200 baud, it's 87µs. > > Older operating systems -- especially from the era where non-FIFO serial > ports were still standard -- would leave interrupts disabled for extended > periods.
At least for the 6551 cartridges on the Commodore 64/128, they were wired to send NMIs. 57600bps generally worked just fine with later ones like the Turbo232 (the SwiftLink was limited to 38400). The 6551 in the Plus/4 is rigged to send IRQs, but I've not used one for serial communications, so I can't say if it was substantially different in its performance. -- ------------------------------------ personal: http://www.cameronkaiser.com/ -- Cameron Kaiser * Floodgap Systems * www.floodgap.com * [email protected] -- Furious activity is no substitute for understanding. -- H. H. Williams -----
