Very  short a comparision between HAYES-1200 and  HAYES-
              2400  modem will be given and only per command  a  short
              functional recoqnition. First however the Hayes command-
              input  line.  It  starts  with  AT  or  at  (no  mix  of
              UPPER/lower)  and ends with a cariage return from now on
              indicated  with  <CR>.  The  only  exeption  is  the  A/
              command, which needs no <CR>. During commandline editing
              backspace (hex '08') is accepted.  One or more  commands
              can  be given after one leading AT.  The max.  length of
              the input string however is 40 char.
              Blanks can be inserted for more readability.

              Command. What does it. Hayes-1200 Hayes-2400 Return code

              AT       Attention         y          y          OK
              A/       Repeat last comm. y          y      depends
              A        Off hook (ANS)    y          y      none (data)
              Bn       1200 (V22/Bell)   -        n=0-1,1      OK
              Cn       TX off/on         n=0-1      -          OK
              D<modif> Dial              y          y      see modifier
              En       Echo off/on(comm) n=0-1    n=0-1,1      OK
              Fn       Echo off/on(data) n=0-1      -          OK
              Hn       Hook on/off/spec. n=0-2    n=0-1    none (data)
              In       prod.code/prom-cc n=0-1    n=0-2    info
              Ln       Speaker (L/M/H)   -        n=0-2,1      OK
              Mn       Speaker off/on    n=0-2    n=0-3,1      OK
              On       Online            only O   n=0-1    none (data)
              P        Set pulse dial    y          y          OK
              Qn       Result code Y/N   n=0-1    n=0-1,0      OK
              Sr=n     Set reg. r to n   r=0-16   r=0-27       OK
              Sr?      Display reg. r    r=0-16   r=0-27   contents r
              T        Set touch dial    y          y          OK
              Vn       Result code N/W   n=0-1    n=0-1,1      OK
              Xn       Dial process      n=0-1    n=0-4,4      OK
              Yn       Long disconn.     -        n=0-1,0      OK
              Zn       Reset             only Z   n=0-1        OK

              &Cn      DCD on/carrier    -        n=0-1,0      OK
              &Dn      DTR modes         -        n=0-3,0      OK
              &F       Load factory set  -          y          OK
              &Gn      Gaurd tone        -        n=0-2,0      OK
              &Jn      RJ-jack sel.      -        n=0-1,0      OK
              &Mn      Asynch./Synchr.   -        n=0-3,0      OK
              &Pn      Pulse ratio       -        n=0-1,0      OK
              &Rn      CTS mode          -        n=0-1,0      OK
              &Sn      DSR mode          -        n=0-1,0      OK
              &Tn      Test local/remote -        n=0-8        OK
              &V       Display conf/tel  -          y          OK
              &Wn      Write conf. MOS   -        n=0-1        OK
              &Xn      Line clock mode   -        n=0-2,0      Ok
              &Yn      Sel. default prof.-        n=0-1        OK
              &Zn      Store teleph. nr. -        n=0-3        OK

              Remark: n=0-2,1 means, n can be 0,1,2 and 1=default.
                      If n=0 this may ommitted. (ATV0 equal to ATV).
                      All numbers are in decimal (max.=255).

              Dial     What does   Hayes-1200 Hayes-2400
              Modifier it
              P        Pulse dial        y          y
              R        Reverse to ANSW   y          y
              Sn       Dial stored tel.  -        n=0-3
              T        Touch dial        y          y
              W        Wait 2e dialtone  -          y
              .        Pause             y          y
              !        Flash             -          y
              @        Wait for silence  -          y
              ;        Return to comm.   y          y

              The registers.
              Reg.  What does it.       Hayes-1200 Hayes-2400
              S0    Ring to answ.on     0-255      0-255,00
              S1    Ring count          0-255,00   0-255,00
              S2    Escape code         0-127,43   0-127,43 ASCII
              S3    Cariage return      0-127,13   0-127,13 ASCII
              S4    Line feed code      0-127,10   0-127,10 ASCII
              S5    Back space code     0-127,08   0-127,08 ASCII
              S6    Wait for dial tone  0-255,02   0-255,02 Sec.
              S7    Wait for carrier    1-30,30    1-30,30  Sec.
              S8    Pause time comma    0-255,02   0-255,02 Sec.
              S9    Carrier detect time 1-255,06   1-255,06 1/10 Sec.
              S10   Lost carrier time   1-255,07   1-255,14 1/10 Sec.
              S11   DTMF dialing speed  50-255,70  50-255,95 mSec.
              S12   Escape code guard   0-255,50   0-255,50 1/50 Sec.
              S13   UART status reg.    y          y
              S14   Option reg.         y          x'AA'
              S15   Flag reg.           y          y
              S16   Modem test          0-2,0      bit settings
              S17   res.                -          res.
              S18   Modem test time     -          1-255,00 Sec.
              S19   Res.                -          Res.
              S20   Res.                -          Res.
              S21   Bit mapped options  -          00
              S22   Bit mapped options  -          x'76'
              S23   Bit mapped options  -          07
              S24   Res.                -          Res.
              S25   Detect DTR change   -          0-255,05 1/100 Sec.
              S26   RTS to CTS delay    -          0-255,01 1/100 Sec.
              S27   Bit mapped options  -          x'40'

              Remark: 1-255,01 means, range 1 till 255, 01=default.
                      All numbers are in decimal (max.=255).
                      x'76' is hexadecimal.

              Return codes Hayes-1200 Hayes-2400
              Digit  Word
              0      OK       y          y
              1    CONNECT    y          y
              2     RING      y          y
              3   NO CARRIER  y          y
              4     ERROR     y          y
              5  CONNECT 1200 y          y
              6  NO DIALTONE  -          y
              7     BUSY      -          y
              8   NO ANSWER   -          y
              9   reserved    -          -
              10 CONNECT 2400 -          y



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