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?
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...?