CompuServe Thread

Rod, The thing with the serial I/O is the interrupt service time. If an interrupt service routine must be performed for each character received, then 57.6 would require 57,600/10 = 5,760cps…and 1/5,760 would be: 173.6 E-6. That means that the CPU would have to be able to shove everything on the stack and perform the complete interrupt service routine for the character in less than 173 microseconds. Anything which would delay that would cause the loss of a character. (Actually the first character would be overwritten by the next character.) This same thing existed with 38.4Kbps, but the time period allowed was 260 microseconds. Those machines which could not cope at 38.4Kbps will certainly not be able to cope with 57.6Kbps. However, replacement of the standard UART with the 16550 allows reduction of the overhead for character retrieval by using FIFO buffers in the UART. This means that instead of an interrupt being issued and serviced for each character, multiple characters can be fetched with each interrupt. The use of the 16550 should allow most 386 class machines to function reliably at 57.6Kbps, but I have not done any testing on this question yet. As always, it will depend upon the other variables involved: the application being run, the TSRs, disk cache, etc.