Many different way to skin a cat, but sometime, Hserin timeout feature can be handy.

HSERIN 500, main,[WAIT("ACK\r"), SKIP 1, tc_mx, tc_my,SKIP 4, p0, c0, SKIP 2]

OR something like this will also work
Packet VAR BYTE [11]
tc_mx VAR Packet[1]
tc_my VAR Packet[2]
p0 VAR Packet[7]
c0 VAR Packet[8]

HSERIN 500, main,[WAIT("ACK\r"), STR Packet\11]

may looks like a mess of variable, BUT...