SIM900 HW communication getting garbage

[dalow]

I am using the SIM900 GPRS modem with the standard windows hyperterminal.
set up 19200 8n1.
tx and rx connected to d0 and d1 (tried both possibilities since I cannot find if d0 or d1 is rx)
attached signal gnd to signal gnd..

attached 12V pwr light on

push pwr button.... netlight blinks every 3 seconds after some start up blinking. (note: colors are different than wiki documentation. Used location on board to determine proper light)

set up terminal to echo characters
press CR and get random characters no matter which direction rx and tx are configured.
Entered ATE1 and get no response. Just a random character after each button press.
I believe the GPRs modem is working but not communicating properly with the serial port. Probably operator error.
I have done this with other GPRS MODEMS in the past using SIM300 chips and it works.
Can you help?
Thanks

[Alex-w]

hi dalow:
you can follow our wiki,and try it again.
if you use the AT command,does it respond OK?
http://www.geeetech.com/wiki/index.php/ ... PRS_Shield

[dalow]

Ok I read through your wiki paper again. No new information.
I configured the serial jumpers for HW usage according to your wiki paper. Therefore I am using D0 and D1 as Rx and Tx.

I attached D0 and D1 directly to my computer serial port COM1. One of the problems I have is it does not say which is Tx and which is Rx. So I tried each way with similar results. I also connected the signal ground.

Using hyperterminal, I set up for 19200 8n1. Then I play with the settings not knowing which are really critical. When I hit CR I get 1 or 2 non alpha characters. Same when I enter a AT command.

Am I trying to do something that has no hope of working?
Which pin is Tx and which is Rx?
What hyper terminal settings are critical?

I think the GPRS modem is working because I get the proper net light blink at 3000 ms. and I get some sort of return on the terminal.
It is probably an operator error, but there are too many parameters to change so I'd like to have more information to limit the issues.
Thank-you

[Alex-w]

HI:
d0->rx
d1->tx
i want to know that does the sim900 board connect to Arduino?
why the com is 1?
the sim900 can not direct connect to the PC

[dalow]

I wonder why board cannot be connected to computer rs232? Is it the voltages?
My plan is to connect it to psoc so I wanted to first get it to work with Pc.
Is the interface i2c? Or what?

[Alex-w]

yes，the PC's voltages is RS232 level，and the sim900 board is TTL。they can’t connect directly

[dalow]

Thank you. Now I know how to connect to the psoc.
It might be good to add these details to the documentation.

[Alex-w]

hi dalow ：
thank you for your Suggestions