Appendix B

                          APPENDIX B


                    COMMAND / CONTROL WORDS



6551 CONTROL WORD FORMAT


d7             d6,d5          d4                       d3, d2, d1, d0
~~~            ~~~~~          ~~~~                     ~~~~~~~~~~~~~~~

0=1 bit        00=8 bits      0= ext clock             0000=16X ext clock
1=2 bits*      01=7 bits      1=baud rate              0001=50 baud
               10=6 bits                               0010=75 baud
               11=5 bits                               0011=110 baud
                                                       0100=135 baud
                                                       0101=150 baud
                                                       0110=300 baud
                                                       0111=600 baud
          *=1-1/2 bits for 5 bits, no parity           1000=1200 baud
          =1 bit for 8 bits, parity                    1001=1800 baud
                                                       1010=2400 baud
                                                       1011=3600 baud
                                                       1100=4800 baud
                                                       1101=7200 baud
                                                       1110=9600 baud
                                                       1111=19200 baud


6551 COMMAND WORD FORMAT


d7,d6     d5        d4        d3,d2                    d1        d0
~~~~~     ~~~       ~~~       ~~~~~                    ~~~       ~~~
00=odd    0=no par  0= norm   00=RTS hi,Tx int off     Interrupt DTR
01=even   1=par     1=echo    01=RTS lo,Tx int on      0=on      0= hi
10=mark                       10=RTS lo,Tx int off     1=off     1=lo
11=space                      ll=RTS lo,Tx int off,
                              break


Examples:

8+1+none, 300 baud: Command byte = $09, Control byte = $16
8+1+none, 1200 baud: Command byte = $09, Control byte = $18



2651 REGISTER 1 FORMAT


d7,d6          d5        d4        d3,d2               d1,d0
~~~~~          ~~~       ~~~       ~~~~~               ~~~~~~
00=invalid     0=odd     0=no par  00=5 bits           00=sync
01=1 bit       1=even    1=par     01=6 bits           01=X1
10=1-1/2 bits                      10=7 bits           10=X16
11=2 bits                          11=8 bits           11=X64




2651 MODE REGISTER 2 FORMAT


d7,d6          d5        d4             d3,d2 d1,d0
~~~~~          ~~~       ~~~            ~~~~~~~~~~~
not            Tx clock  Rx clock       0000=50 baud
used           0=ext     0=ext          0001=75 baud
               1=int     1=int          0010=110 baud
                                        0011=135 baud
                                        0100=150 baud
                                        0101=300 baud
                                        0110=600 baud
                                        0111=1200 baud
                                        1000=1800 baud
                                        1001=2000 baud
                                        1010=2400 baud
                                        1011=3600 baud                     
                                        1100=4800 baud
                                        1101=7200 baud
                                        1110=9600 baud
                                        1111=19200 baud


Examples:

8+1+none, 300 baud:  Command byte = $4E, Control byte = $35
8+1+none, 1200 baud:  Command byte = $4E, Control byte  $37



6850 COMMAND WORD FORMAT


d7                  d6,d5                    d4,d3,d2            d1,d0
~~~                 ~~~~~~                   ~~~~~~~~            ~~~~~

0=int disabled      00=RTS lo, Tx int off    000=7+2+even        00=X1
1=int enabled       01=RTS lo, Tx int on     001=7+2+odd         01=X16
                    10=RTS hi, Tx int off    010=7+1+even        10=X64
                    11=RTS lo, break         011=7+1+odd         11=reset
                                             100=6+2+none
                                             101=8+2+none
                                             110=8+1+even
                                             111=8+1+odd

Example:
8+1+none:  Command byte =$95



8251 MODE INSTRUCTION WORD FORMAT


d7,d6          d5        d4        d3,d2               d1,d0
~~~~~          ~~~       ~~~       ~~~~~               ~~~~~~
00=invalid     0=odd     0=no par  00=5 bits           00=sync
01=1 bit       1=even    1=par     01=6 bits           01=X1
10=1-1/2 bits                      10=7 bits           10=X16
11=2 bits                          11=8 bits           11=X64

Examples:

8+1+none, 300 baud:  Command byte = $4E, Control byte = $01
8+1+none, 1200 baud: Command byte = $4E, Control byte = $03



8530 (IIGS) COMMAND WORD FORMAT


d7,d6          d5,d4          d3,d2               d1,d0
~~~~~          ~~~~~~         ~~~~~               ~~~~~~
00=5 bits      0  0           01=1 stop           00=no parity
01=7 bits                     10=1.5 stop         01=odd parity
10=6 bits                     11=2 stop           10=no parity
11=8 bits                                         11=even parity


8350 (IIGS) CONTROL WORD FORMAT


Value          Baud Rate
~~~~~          ~~~~~~~~~

$01            50
$02            75
$03            110
$04            135
$05            150
$06            300
$07            600
$08            1200
$09            1800
$0A            2400
$0B            3600
$0C            4800
$0D            7200
$0E            9600
$0F            19200


Examples:

8+1+none, 300 baud:  Command byte = $C4, Control byte = $06
8+1+none, 1200 baud:  Command byte = $C4, Control byte = $08
8+1+none, 2400 baud:  Command byte = $C4, Control byte = $0A