Commodore modem 300 User Manual page 75

Todetect carrieron theVIC20, thefollowing statement can be used
in a BASIC program:
OH = 37136:
IF((PEEK(OH) AND 16) = 16)THEN PRINT"NO CARRIER" :
IF((PEEK(OH) AND 16) = 0) THEN PRINT"CARRIER DETECTED"
It is not possible to detect carrieron the Plus/4 computer. In fact,
the Modem/300 will not work at all on the Plus/4 without modifica­
tion. If you have a Plus/4 and would like to use the Modem/300, a
solder jumper on the bottom of the modem near the edge connector
must be opened. Be aware, however, that if you attempt this modifi­
cation yourself, you will void your warranty. This modification
should only be undertaken by qualified Commodore service
personnel.
ROTARY (PULSE) DIALING
In order to dial a number with the Modem/300, the software in the
computer must generate pulses at a prescribed rate. In the United
States and Canada, the rate is between 8 and 10 pulses per second
with a 58% to 64% break duty cycle. Most people, however, use 10
pulses per second, with a 60% break duty cycle.
To make a call, your software must first take the phone " off hook"
(the equivalent of you picking up the receiver). Then to dial the first
digit, a 3 for instance, the software must put the phone on hook for
60 milliseconds, and off-hook for40 milliseconds. Repeat this pro­
cess 3 times to dial a 3.
The same method is used to dial all other digits except 0, which is
pulsed 10 times. Pause at least 600 milliseconds between each
digit.
USING THE MODEM/300 WITH THE
COMMODORE 128
The Modem/300 is used with the Commodore 128 in 64 mode the
same way it is used with the Commodore 64. In 128 mode, BASIC
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