NorthStar HORIZON Manual page 64

5. If the data wr i te case then
a. issue begin write command.
b. wait for WI status bit to be false.
c. write 15/31 bytes of zeros.
d. write the sync character (s) (FB hex)
e. write 256/512 bytes of data from RAM while computing the
cyclic check character.
f. write the check character.
g. if more blocks to write on the same track then wait until
the next sector pulse and repeat from step a, otherwise
done.
6. I f read case then
a. wait for RE to be true and test DO status bit.
b. wait for sync character detection (i.e. body "lode). Report
an error if the sync character is not detected.
c. read 256/512 ¢ata bytes into RAM while computing the check
character.
d. read the check character and compare with the computed
check character. Report an error if they are not equal.
e. if there are more blocks to read on the same track then
wait until the next sector pulse and repeat from steD a,
otherwise done.
7. If verify case then all is the same as the read case except
that in step c data bytes read from the disk should be
compared for equality with the data in RAM. Report an error
if corresponding bytes do not compare.
DISK CONTROLLER INTERRUPTS
The software provided with the disk system is not interrupt
driven. The controller can cause an interrupt on anyone of the
interrupt lines on the S-100 bus by connecting the appropriate
jumper at the lower left corner of the controller board. An
interrupt will be generated at every sector pulse while the
interrupt is armed in the controller. See the COMMANDS section
for details of interrupt arming and disarming. Special user
generated, interrupt driven software can be written which uses
the controller sector pulse interrupt.
Before the .low level controller software is
call~d,
interrupts
should be disabled. If an interrupt occurs during data
transmission then data can be lost as a result of excessive delay
in the interrupt routine.
North Star HORIZON Computer
64