sim900 transparent mode and cts signal

[lco]

Hello!

I can succesfuly connect to the server with sim900 using transparent with tcp. I have hardware(cts/rts) flow control enabled. But, after sending last byte and inbetween when waiting for recommended 1000ms and before sending the "+++" sequence, CTS signal goes high, like:

: connect to the server, transparent mode, escape sequence enabled, tcp, hardware flow control, etc..
: send some data (several bytes)
: wait for 1000ms, after several 100ms cts goes high and stays that way until server responds or closes connection due to the inactivity
: if i disregard cts line after delay of 1000ms time and send +++ anyway it exits data mode, but +++ escape sequence is still visible on the server

Although i can avoid this by not using hardware flow control or just ignoring the cts line at that time i would really like to understand this behaviour. Is this default beahaviour of cts signal on the sim900? It just seems to go against my reasoning . Thank you!

 

[suha123]

hi,
Even iam facing d same problem.Can anyone suggest the solution for this.

Thanks in Advance.

 

[sabeti_1990]

yes it is
it may because of bad firmware code on module
did U try sim300 it seem so better

 

[mihairainer]

I had same problem. The problem is a combinated one.
First, SIM900D doez not accept a command until it executes the previous one.
Also, it does not execute a command if it is nont finished and you will
send another command to the device. Shortly, you MUST wait
the respone from modem after each command.
Also, you have to enable hardware flow by using AT+IFC=2,2\r\n
Using this strategy helped me to solve a similar issue.

Best regards,
Mihai

Hello!

I can succesfuly connect to the server with sim900 using transparent with tcp. I have hardware(cts/rts) flow control enabled. But, after sending last byte and inbetween when waiting for recommended 1000ms and before sending the "+++" sequence, CTS signal goes high, like:

: connect to the server, transparent mode, escape sequence enabled, tcp, hardware flow control, etc..
: send some data (several bytes)
: wait for 1000ms, after several 100ms cts goes high and stays that way until server responds or closes connection due to the inactivity
: if i disregard cts line after delay of 1000ms time and send +++ anyway it exits data mode, but +++ escape sequence is still visible on the server

Although i can avoid this by not using hardware flow control or just ignoring the cts line at that time i would really like to understand this behaviour. Is this default beahaviour of cts signal on the sim900? It just seems to go against my reasoning . Thank you!

 

[devil6600]

I had same problem. The problem is a combinated one.
First, SIM900D doez not accept a command until it executes the previous one.
Also, it does not execute a command if it is nont finished and you will
send another command to the device. Shortly, you MUST wait
the respone from modem after each command.
Also, you have to enable hardware flow by using AT+IFC=2,2\r\n
Using this strategy helped me to solve a similar issue.

Best regards,
Mihai

Hi Mihai,

i have connected CTS/RTS line, but when ever i try to put CTS line low to suspend data transmission it doesn't stop and my microcontroller gets overflow. i have also tried putting AT+IFC=2,2 and i got OK response but it seems sim900 is not supporting hardware flow control. just to confirm my setup, i have connected TX,RX,CTS,RTS line to my microcontroller, is there i am missing something?

thank you