Modes 1-6 & 8.
PSI BOX Reference
Addressed Operation.
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The address of the RS232 input output port is as set on the
IEEE address DIP switches. The Centronics port address is one
greater than the RS232 address.
The description of the RS232 port is identical to Mode 1.
Any data sent to the Centronics port is buffered in the PSI
BOX. The PSI BOX sends this buffered data when the
Centronics handshake permits. If the Centronics output buffer is
full then the IEEE handshake will freeze, with NRFD and
NDAC held low, waiting for the Centronics device to become
ready to receive the contents of the PSI BOX buffer. This
ensures that no data is lost!
Attempts to data read from the PSI BOX Centronics port
causes the ’talk with nothing to say’ message to be sent, this is
the 00 byte with EOI true, since in Mode 2 the Centronics port
is OUTPUT only. This prevents a hang-up in the handshake.
In Mode 2 half the PSI BOX ram acts as the Centronics
output buffer, the other half is evenly split between the RS232
input and output buffers.
Pet To PC Ascii Conversion.
_________________________
Commodore Pet to PC Ascii conversion will be performed
depending on the state of mode DIP switch 8. When the switch
is UP, ie ON, all out going data to the RS232 port and the
Centronics port will be converted from the Pet character to
standard PC Ascii. All input via the RS232 port will be
converted from PC Ascii to Petscii. The output conversion is
generally used to connect standard Centronics or RS232 Ascii
printers to CBM Pet or C64/128 computers.
Unlike all other PSI BOX modes, in Mode 2 the state of
DIP switch 8 IS monitored whilst the PSI BOX is in operation.
This means that the conversion can be switched in and out at
will whilst the PSI BOX is on. Data already in the buffer will
not be changed only the new incoming data will be converted
according to the setting of DIP 8.
Chapter 6
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