The following code works. Serin2 modes differ from serin modes, and I think the variables for serin and serout ports have to have numbers.

DEFINE OSC 20

S0 var portb.0 ' Define serial out pin
S1 var portb.1 ' Define serial in pin
RDR1 VAR portb.3 ' serial in from reader
RST1 VAR portb.2 ' reader reset
B0 var byte 'byte variable
tag var BYTE[10] ' Creates a byte array of 10 bytes

HIGH RST1 'reset Reader

loop: Serin S1,6,B0 ' B0 = input character
PAUSE 1500 'wait a sec
Serout S0,6,["ready "] 'Send ready
SERIn2 RDR1, 16468,[skip 2, STR tag\10] 'read in tag ID
SEROUT S0,6,["got the code: "] 'acknowledge
print: Serout2 S0,16468,[STR tag] 'send out tag ID
Serout S0,6,[" done"] 'print done
Goto loop 'do it again