Below is the picture of the modem



In the Picture it is connected to PC's RS232 Port directly.
I can communicate to it using MikroC Pro's USART Terminal.

So far I can call and send sms.

I am gonna connect this modem to a PIC's USART.
Question is to Send Data and to check the modems respond what terminal (like CTS) needs to be connected to PIC besides TX and RX ?
And Do I need a RS232 level converter (such as MAX232) between PIC and Modem ?
If yes (MAX232) Do I need to converter all the levels besides TX and RX ?

 

Most RS232 communication now does not use a populated Null Modem cable, just the three lines RX/TX/ and GND.
If necessary the handshake can be jumpered 1-4-6 & 7-8
The MAX232 and equivalents will interface the Pic.
Usually the pic will monitor the interrupt for receiving the speed of which does not require hardware handshake.
With full populated Null Modem all have to be level converted.
If H.S. is required, it is usually done with a S/W H.S. such as XON/XOFF code.
Max.

 

Since you do direct connection to pc, this tells me that you have +/- 15 volts signals. Which in turn tells me that you need MAX232 to convert those 15 volt signals into 5 volt signals that PIC uses.

 

OK....what about any extra pins that is needed ?

 

What RS232 baud rate are you using?
9600 is common but even if using the 115200 that usually does not require hand shake with modern high speed communication methods.
If uncertain, what I would do is use the common 2 pins, TX & RX and jumper the handshake out as I posted in #2. and see if you get good communication without loss of data.
Or if doubtful, use 9600 baud.
Max.

 

Modem is compatible with 9600 and 115200 baud. No problem.
Modem manual says.
115200 Baud, 8 data 1 stop, no parity. no flow control

 

I will check only using RX and TX then add any extra pins one by one.
Or remove one by one and check the communication

 

If you have a fully populated null-modem cable that you don't want to modify, you can jumper out at the Pic end.

Max.

 

I will look into this.
Thanks Max.

 

I checked the Maestro with just TX and RX connected to com port and it still works.
I can see signal strength and SIM status plus network plus send SMS

So, is it safe to assume that I do not need any other connections to PIC to check and do the above ?

 

Looks so, also you may not need the 9D socket jumpers on the Pic end.
Max.

 

You mean 9 pin headers ?

 

I was referring to the Sub-D socket as in the picture (should show a 9s not 9p) , usually used to accommodate a pre-wired RS232 cable.
It shows pins jumpered.
Max.

 

I need to buy that.

 

I guess you can use any plug or socket or termination you care to.
It is just that it is useful to use a 9D socket if you have a standard Null-Modem cable.

The original RS232 modem used a 25pin D socket and plug each end, now 9D pin.
The 'Computer' end was termed DCE, Data Computer Equipment, the device end was DTE, Data Terminal Equipment.
Main controller end is 9P (plug) and the peripheral end is 9S (socket).
All this handshake business was because originally the main control was a PC and the peripherals such as tape punch and tape reader, teletype etc usually had a LSI ic USART so there was minimum processing intelligence on board, so extra lines were included to show the condition of the peripheral and for the PC to turn on/off the punch etc.
Now with most peripherals also having powerful/fast processors, it is generally not needed.
Max.