#!/bin/bash
PORT="/dev/ttyAMA0"

SYNC=a0 #BYTE1
ADDR=01 #BYTE2
BYTE3=${1:-0}
BYTE4=${2:-0}
BYTE5=${3:-0}
BYTE6=${4:-0}
BYTE7=af
SUM=0  #BYTE8

# Count SUM
hex=''
for i in $* ; do hex+="0x$i "; done
a="0x$SYNC 0x$ADDR ${hex}0x$BYTE7 " # $hex contains space as last char
SUM=$(eval printf %x $(( ( ${a// /^} 0x0 ) & 0xff )) )

echo "Pelco 'P': $SYNC $ADDR $BYTE3 $BYTE4 $BYTE5 $BYTE6 $BYTE7 $SUM"

# Write to port
printf "\x$SYNC\x$ADDR\x$BYTE3\x$BYTE4\x$BYTE5\x$BYTE6\x$BYTE7\x$SUM" > "$PORT"