Instruction Manual

Logic Functions - Book 1
APPENDIX B - MODBUS MASTER CONFIGURATION
B-7
INPUT5 NUM OF MM EX BLKS CFGD OK Local Count
Not writeable through message handler.
This value indicates the number of Modbus Master EX blocks that are
configured with no errors and have ram space allocated.
Value 65534 indicates there is more than one of these EX blocks configured
for this modbus master port; therefore, this one is not used.
Value 65535 indicates the port that this EX block is configured for is not a
modbus master port.
INPUT6 RESPONSE TIMEOUT Local Long State
This parameter specifies the amount of time (in 50 ms units) that the driver
waits for a response message from the slave device. Valid values are 2
through 255. If there are more than one of these EX blocks in the database
the lowest occurrence number EX block will be used.
Determine the maximum time the various slave devices take to respond to a
message (a Modcell Multiloop Processor will respond within 100 milliseconds
and a Modcell 2050R will respond within 250 miliseconds). Next, determine
the RIR (Read Input Register) or RHR (Read Holding Register) message that
requests the largest number of registers for each of the different slave
devices. Now use the following formula to calculate the response timeout for
each slave device (use the largest value plus some additional slop time).
BAUDRATE BUS TIME PER CHARACTER (12 bits maximum)
38400 0.312 milliseconds
19200 0.625 milliseconds
9600 1.250 milliseconds
4800 2.500 milliseconds
2400 5.000 milliseconds
1200 10.000 milliseconds
600 20.000 milliseconds
300 40.000 milliseconds
150 80.000 milliseconds
OVERHEAD = 8.5 Characters (addr, mfc, byte cnt, 2 crc, 3.5 char idle for
EOM)
TOTAL # CHARACTERS = (Number Registers Requested x 2) +
OVERHEAD
BUS TIME = TOTAL # CHARACTERS x BUS TIME PER CHARACTER
TOTAL RESPONSE TIME = BUS TIME + Respone Time of Slave Device +
Slop
RESPONSE TIMEOUT VALUE = TOTAL RESPONSE TIME / 50
INPUT7 NUMBER OF RETRIES Local Long State
This parameter specifies the number of times a message should be re-sent to
a slave following an invalid or no response message from the slave. Valid
values are 0 through 255.