Hello I need to communicate gsm module. as it use asci AT commands I ask if I can connect the modems serial port directly to the microcontroller such as 89s51/8051 or I need interface?
As always, you need to read the Datasheets for both the microcontroller and the GSM module - that will tell you whether the two devices are directly compatible, or if some sort of interface is needed.
Cross-posted with 8052.com www.8052.com/.../161719
There is nothing in the datasheets on this
See your cross-post at 8052.com - although the specific title given to the document may not actually be "datasheet", there most certainly must be a document that specifies this!
On the other hand, if the product is so poorly documented that such basic, essential information as this is so hard to find - do you really want to waste your time on it...?