The system message routines 

Finally there follow some messages. A message follows directly after the CALL to the ROM
print routine.

304B MSG_0      CALL #178A,PO_MSG1
304E            DEFM "* MGT PLUS D DISC"
3060            DEFB " "+128
3061 MSG_1      CALL #178A,PO_MSG1
3064            DEFM " CATALOGUE *"
3070            DEFB 13,13+128
3072 MSG_2      CALL #178A,PO_MSG1
3075            DEFB 13,13
3077            DEFB "Number of Free K-Bytes ="
308F            DEFB " "+128
3090 MSG_3      CALL #177E,PO_MSG
3093            DEFM "©Miles Gordon Technology G+DOS2a"
30B3            DEFB 13,13+128

This routine makes sure the 'SOURCE' and 'TARGET' messages are printed in turn.

30B5 TO_MSG1    LD   A,(#3107)
30B8            XOR  #01
30BA            LD   (#3107),A
30BD            JR   NZ,#30E3,MSG_5
30BF MSG_4      CALL #178A,PO_MSG1
30C2            DEFB 13
30C3            DEFM "Insert SOURCE disc - press SPAC"
30E2            DEFB "E"+128
30E3 MSG_5      CALL #178A,PO_MSG1
30E6            DEFB 13
30E7            DEFM "Insert TARGET disc - press SPAC"
3106            DEFB "E"+128

3107            DEFB #00

THE 'CLEAR MESSAGE FLAG' SUBROUTINE

3108 TEST_SAVE  XOR  A                   Clear the flag used in printing
3109            LD   (#3107),A           'SOURCE' and 'TARGET' message.
310C            CALL #1635,TEST_5
310F            RET