Texas Instruments 990 Operation Manual page 100

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Result: The Open supervisor call is ignored except by the tape cassette, for which it forces a
playback/record initialization. When a LUNO outside the range 0 to F
16
is specified, the
command is ignored.
3.5.2.2 Read ASCII. The Read ASCII supervisor call reads ASCII data from an input device.
Supervisor call code: 0
I/O operation code: 9
Calling parameters:
luno
buffer addr
buffer length
char count
Logical unit number of a device from which
data is to be read.
Absolute memory address of the first byte
of an input buffer.
Maximum length of the input buffer.
The number of characters actually transferred.
This value is returned by the supeIVisor.
Result: Data
is
read from the specified device until either the buffer length is satisfied or a
terminating event such as a carriage return occurs. A read from a dummy device will cause the
end-of-file flag to be set.
Errors: An unrecoverable I/O error is returned if:
• An I/O error occurs.
• The output cassette is not ready.
3.5.2.3 Write ASCII. The Write ASCII supeIVisor call writes ASCII data to an output device.
Supervisor call code: 0
I/O operation code: B
Calling parameters:
luno
buffer addr
buffer length
char count
Logical unit number of a device to which
data can be written.
Absolu te memory address of the first byte
of an output buffer.
Unused.
The number of characters to be transferred.
Result: Data is written to the specified device until the character count is satisfied. If the
character count is greater than 80 when writing to a cassette, only the first 80 characters are
written to cassette.
3-62
Digital Systems Division