With just a 3 byte buffer the whole thing could be non blocking,
and the 1 timeout might even be able to be changed to zero for no delay at all.

Code:
buffer var byte[3]
inputbyte var byte

main:
'
HSERIN 1,nodat,[inputbyte]	‘ receive next byte
buffer[2] = buffer[1]		‘ rotate into buffer
buffer[1] = buffer[0]
buffer[0] = inputbute
if (buffer[2] = 176 && buffer[1] = 44) then
if buffer[0] = 69 then portb.0 = 1
if buffer[0] = 5 then portb.0 = 0
endif
nodat:				' timeout label for no byte received
'
// the rest of the program
‘
goto main