Hello
I wrote a MODBUS routine which sends some readings over RS485 to a PLC(currently a PC RS232 port).
My SETUP ->
I have a PCMCIA-RS232 on my notebook PC.
MBPOLL utility on PC.
Microcontroller running all code.
MAX232 level shifter.
SN75176 (485 comm) as Half duplex with direction control with MCU Port pin.
RS485-RS232 converter.
What works ->
Direct 232 connection from MAX232 to PC works and MBPOLL is happy with no errors.
What doesn't->
When i use MCU->SN75176->485-232 converter->232-PCMCIA->MBPOLL
MBPOLL is not happy with timeout errors.
Whenever i am transmitting , i push the DIR port-pin high (DE-RE on SN75176 shorted and connected to this pin)
all the other time, this pin is low.
I saw that my MCU receives the requests from the MASTER in the buffer, and updates the response values immediately in the buffer.It just doesn't get through.
I have terminated the A-B lines with a 120Ω resistor.
Earlier I have tried pulling up B line and pulling down A line to no avail.
I can see communication with a DSO , and see that the DIR pin is high for all the transmit waveform and low for the receive.
Please guide me, whether i am missing some point, or anything more needs to be done.
Thanks and regards
I wrote a MODBUS routine which sends some readings over RS485 to a PLC(currently a PC RS232 port).
My SETUP ->
I have a PCMCIA-RS232 on my notebook PC.
MBPOLL utility on PC.
Microcontroller running all code.
MAX232 level shifter.
SN75176 (485 comm) as Half duplex with direction control with MCU Port pin.
RS485-RS232 converter.
What works ->
Direct 232 connection from MAX232 to PC works and MBPOLL is happy with no errors.
What doesn't->
When i use MCU->SN75176->485-232 converter->232-PCMCIA->MBPOLL
MBPOLL is not happy with timeout errors.
Whenever i am transmitting , i push the DIR port-pin high (DE-RE on SN75176 shorted and connected to this pin)
all the other time, this pin is low.
I saw that my MCU receives the requests from the MASTER in the buffer, and updates the response values immediately in the buffer.It just doesn't get through.
I have terminated the A-B lines with a 120Ω resistor.
Earlier I have tried pulling up B line and pulling down A line to no avail.
I can see communication with a DSO , and see that the DIR pin is high for all the transmit waveform and low for the receive.
Please guide me, whether i am missing some point, or anything more needs to be done.
Thanks and regards