PIC16F877A and SIM300CZ problem connection

Dear all,

please help me.

I used PIC 16F877a to send and read SMS via SIM300.
Serial connection:
PIC_TX -> SP3238 -> SIM300_RX
PIC_RX <- SP3238 <- SIM300_TX
Sim300_RTS -> GND

I read/send SMS via SIM300 OK but I send SMS -> Read SMS -> Read SMS(fail)

I don't read SMS again after send SMS. You can help me.

Thanks.

Dear All,

I add information of connection between PIC and SIM300, please help me.

I connected SIM300_RTS -->GND, baud rate of of SIM300 are fixed 9600, PIC_UART baud rate are 9600

Thanks.

Visit this topic and download the file called serial_port.pdf. May be can help you.

Thanks for your reply.

I connected same as schematic in Serial_Port.pdf.
Current i send AT command (AT+CMGR=1) to read sms from PIC16F877A, i receive response of SIM300 but this response is not same as specification in file "SIM300C AT.PDF" , "item 1.4" page 5, i receive AT command read (AT+CMGR=1) in top of buffer (buffer store SMS in PIC16F877A).

Detail:
- send from PIC16F877A
AT+CMGR=1\r
- wait to get response from SIM300
- content of buffer after get response
AT+CMGR=1\r\r\l+CMGR: "REC READ"\r\lSMS_content\r\l\r\lOK\r\l

specification in file SIM300C AT.PDF, response must be:
r\l+CMGR: "REC READ"\r\lSMS_content\r\l\r\lOK\r\l

I don't know why i get "AT+CMGR=1\r" string in buffer, I try with another command, the result is same. You can explain?

Note: i have a sms in Sim card.

After i read SMS, sent SMS OK, i read SMS again fail, please help me.

Thanks
duyha

I think you have echo mode active.
Disable it with ATE0.

Dear hoodooman,

I sent AT0 command, it is OK, thank you very much.

Regard.

Have you sent at command "AT+CMGF=1" yet?

Dear Angel_eyes,

I sent AT+CMGF=1, and store this setting in flash of SIM300C, I send and receive SMS OK.

Regards.

Is that an RS232 transceiver you have there? Is it absolutely necessary? You could just use open drain buffers with pullups.

I use LJ245A to convert logic level between PIC16F877A and SIM300.