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statement, within a program, only this number need be used
in the following inputfoutput statements. This eliminates the
need for further restatement of device number, secondary
address (where used) and file name (where used).
Although it is permissable to identify and use many logical files in a given program, the PET operating
system has to keep track of the files that are currently in use in the program. The greatest number of files
that can be controlled by the PET at one time is ten. Note that exceeding ten will result in loss of PET
operation; this can be restored by switching the computer off and on. A logical file number can be any
integer in the range 1 through 255.
Device
Keyboard
Cassette 1 panel mounted
Cassette 2 add-on
Video screen
o
Default- 1
2
3
DEVICE NUMBERS
All devices which the PET communicates with are assigned numbers. The first four of these are reserved
for the following peripherals:
Device
Number
All other devices are automatically assumed by the PET to be IEEE devices, and control is transferred to
the device which will have been allocated a number within the range 4 through 30. Except in special
cases, a specific number would be allocated to each IEEE device to allow the PET and a particular device
to communicate using the parallel IEEE-488 bus.
On many IEEE devices, the allocation of the device number is made by means of a switCh, or in the case
of less expensive products, by the connection of jumpers.
Operation
Normal printing
Printing under format statement control
Transfer data from PET to format statement
Set variable lines per page
Use expanded diagnostic messages
Byte data for programmable character
SECONDARY ADDRESSES
The concept of secondary address may be new to those people who have never worked with the IEEE bus.
The use of a secondary address permits an intelligent peripheral to function in anyone of a number of
modes. For example, in a PET printer, there are six secondary addresses:
Secondary
Address
DefaUlt- 0
1
2
3
4
5
In short, by changing the secondary address used to communicate with a given physical device, its
operating characteristics can be totally changed, if so desired. Many of the IEEE devices have their own
particular secondary address conventions which must be followed. Specific data on these conventions
can be obtained by conSUlting the manual for that particular device.
Operation
Tape is being opened for "read"
Tape is being opened for "write"
Tape is being opened for "write" with an "end of
tape" header being forced when the file is closed.
The PET tape un!ts have a special set of secondary address rules:
Secondary
Address
Default- 0
1
2
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