Beijer Electronics SCOM Protocol EN - Manual (Page 138)

Sample Communication Application
138 Elektronik-Systeme Lauer, MAEN976
/*=====================================================================*/
/* SCOM limits. */
#define _SCOM_MSG_HDR_SIZE 7
#define _SCOM_MAX_MSG_LEN 82
#define _SCOM_MAX_DAT_LEN 74
/* SCOM attention codes. */
#define _ATTN_CMD 0x07
#define _ATTN_ACK 0x06
#define _ATTN_NAK 0x15
/* SCOM message fields. */
#define _SCOM_MSG_OFS_ATTN 0x00
#define _SCOM_MSG_OFS_ADDR 0x01
#define _SCOM_MSG_OFS_CMD0 0x02
#define _SCOM_MSG_OFS_CMD1 0x03
#define _SCOM_MSG_OFS_CMD2 0x04
#define _SCOM_MSG_OFS_LEN 0x05
#define _SCOM_MSG_OFS_ICHK 0x06
#define _SCOM_MSG_OFS_DATA 0x07
#define _ "\r\n"
/*=======================================================================
Calculates and returns the inverse header checksum of the provided SCOM
message.
*/
unsigned char
getICHKH(unsigned char *pucSCOM)
{
unsigned char uc;
unsigned char ucICHKH;
/*========*/
ucICHKH=0;
for (uc=0;uc<=5;uc++)
ucICHKH+=pucSCOM[uc];
return ~ucICHKH;
}
/*=======================================================================
Calculates and returns the inverse data checksum of the provided SCOM
message.
*/
unsigned char
getICHKD(unsigned char *pucSCOM,unsigned char ucLen)
{
unsigned char uc;
unsigned char ucICHKD;
/*========*/
ucICHKD=0;
for (uc=_SCOM_MSG_OFS_DATA;uc<_SCOM_MSG_OFS_DATA+ucLen;uc++)
ucICHKD+=pucSCOM[uc];
return ~ucICHKD;
}