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6
V550-A20 Operation Manual
Section
5-
6
Appendices
Timing
If a slave unit is going to respond to a poll from the master, it must start its
response within two character times of the end of the carriage return at the
end of the poll.
NOTE:
This makes the response time dependent upon the baud rate.
The slave must turn on its transmitter within two character times after
receiving the CR of the master's poll. The slave must place the STX at the
beginning of its response, into its serial port no later than three character
times after receipt of the master’s carriage return.
Once the slave begins transmitting, it must not allow a gap of more than one
half a character time between characters. Most transmissions will take place
under interrupt, so this should not be a problem; however, it means that
serial port interrupts may not be disabled for an extended period of time
during data transmission.
Master:
Time:
Slave:
RTS
TXD
S0123456Ps
(CR)
B
A
C
RTS
TXD
S0123456PsS0123456Ps_________S01
(FFh) (STX)
“S” is the start bit, “0123456” are the character bits, “P” is the parity bit and
“s” is the stop bit.
Typically, the “RTS” line is used to control the transmitter. In this diagram,
“RTS” is high when the transmitter is enabled and low when the transmitter
is disabled (“tri-stated”).
NOTE:
The slave’s “FF” may be replaced with a 1 character time (10/baud
rate) delay between transmitter turn-on and transmission of the STX.
Time Limits:
A
Maximum: 2 character times (20/baud rate).
Minimum: 0.
Summary of Contents for V550-A20
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