Commodore 2001-8 User Manual page 85

130 IF ST=2THEN 400 time out with no errors
Each error can noW be processed with the following:
140 IF ST AND mask THEN Mask represents the bit being tested
POLLING TECHNIQUES
One technique to poll slow IEEE·488 devices such as sampling devices, which take many minutes to
respond, is to use the INPUT# from the device; then if the status indicates time out, process other
routines or loop on the INPUT # until no error occurs. If there are no errors, the correct data has been
finally read and one can process that data information.
By using this sampling technique, a whole series of slow devices can be serviced, along with running a
foreground program
by
use of the real time clock (Tl,TI$) and the INPUT#ltimeout error sequence, to
occassionally poll devices.
DEFAULT PARAMETERS
Parameter Default Value
Default Operation
Device
:#
0'=1
Cassette #1 selected
Secondary
SA=(jI
On tape files open for read
address
On IEEE-488 devices, no
secondary address is sent.
Table 7.18. Default values.
Equivalent
Statement
(Default) Operation
Parameter Values
OPEN
1
OPEN 1,1,0
Open logical file #1 for cassette #1 read
'---"
no file name
-
' . -
- -
OPEN
1,2
OPEN it l,2,0
Open logical file #1 for cassette #2 read
no file name
OPEN 1,2,1
OPEN#1.2,1
Open logical file #1 for cassette
#2
write
no file name
OPEN 1,2,1, OPEN#1,2,1,
Open logical file #1 for cassette
#2
write
"OAT" "OAT" file named "OAT"
Table 7.19. Example of default parameters.
INTRODUCTION TO THE IEEE'488 BUS
This bus consists of 16 signal lines that are divided functionally into three groups, those are:
a) The data transmission bus
2) The control bus
3) The management bus
Furthermore, the IEEE bus can support three classes of device:
a) Talkers: at any given moment, only one device is permitted to transmit
data to the data bus.
b) Listeners: as many devices as required may receive data
simultaneously from the bus,
c) Controllet: the PET is the
only
controller allowed on the IEEE bus.
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