DIGITAL-LOGIC Microspace MSM586SEN Technical User Manual page 148

DIGITAL-LOGIC AG
4.3.3.1.3
It is a lot easier to get the RTS turn-off timing exact under MS-DOS than under Windows. Under MS-DOS,
simply wait for both the TX-buffer-empty and all-sent UART flags to go true and then drop RTS. Under Win-
dows, you can use various timing methods (none of which will be precise) or configure the converter to have
its receiver always enabled (so you receive your own transmit data) and when you have received the last
character of your transmission, drop RTS. The required RTS turn-off accuracy depends on how fast the
slave device responds; if it starts transmitting its response within 1 bit of the end of your transmission then it
may be impossible to do this under Windows and an ADE converter will be required. If however it does not
start its response for e.g. 10ms then (at 9600 baud) a simple timer should be sufficient. The Windows NT
(and higher) comms API offers a "RTS control" function but this is reliable only to within 10ms or so. KK Sys-
tems user-programmable products (KD485-PROG and PPC) contains special functions to assist with precise
driver turnoff.
4.3.3.1.4
If you are a software developer:
RTS Control – Illustration
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MSM586SEN/SEV Manual V1.5E