' {$STAMP BS2}
' {$PBASIC 2.0}
'               DTMF Decode
'            with mt8880 chip
'   
'
rs CON 4
rw CON 5
cs CON 6

dtmf VAR Byte                  ' received dtmf digit
dt_flag VAR Bit                ' dtmf received flag
dt_det VAR INL.BIT2            ' dtmf detected status bit
polls VAR Word                 ' # of unsuccessful polls of dtmf
sp_time CON 1500               ' print this # of polls w/o dtmf
n24n CON $418d                 ' serout constant: 2400 baud inverted

' initialise the mt8880 for receive

OUTL=%0111111                  ' pin 7 (LCD) low,pins 0 to 6 high
DIRL=%1111111                  ' set up to write to mt8880 (all outputs)
OUTL=%00011000                 ' set up reg A, next write to reg b
HIGH cs
OUTL=%00010000                 ' clear reg B,ready to send dtmf
HIGH cs
DIRL=%11110000                 ' now set the 4-bit bus to input
HIGH rw                        ' and set rw to "read"

again:
PAUSE 100
HIGH rs                        ' read status reg
LOW cs                         ' activate the mt8880
dt_flag=dt_det                 ' store dtmf-detected bit into flag
HIGH cs                        ' end the read

IF dt_flag=1 THEN skip1        ' if tone detected then continue
polls=polls+1                  ' another poll without dtmf tone
IF polls<sp_time THEN again    ' if not time to print space,poll
dtmf=16                        ' tell display routine print a space
GOSUB display                  ' debug

skip2:
polls=0                        ' clear the counter
GOTO again                     ' poll some more

skip1:                         ' tone detected
polls=0                        ' clear poll counter
LOW rs                         ' get the dtmf data
LOW cs                         ' activate mt8880
dtmf=INL & %00001111           ' strip off upper 4 bits using AND
HIGH cs                        ' de activate mt8880
GOSUB display                  ' display data
GOTO again                     ' do it all again

display:
DEBUG DEC dtmf
ret:
RETURN
 