transmitting int8???

hi to all

this is the API in Zstack SampleApp.c to send the uint8 type data

here how i can transmit int8 type data ?????
 
    AF_DataRequest( &LocationInfo_DstAddr, &SampleApp_epDesc,
                         SAMPLEAPP_PERIODIC_CLUSTERID,
                         3,
                         (uint8*)&id,
                         &SampleApp_TransID,
                         AF_DISCV_ROUTE,
                         AF_DEFAULT_RADIUS);

help me ........