Scorpio News |
April–June 1987 – Volume 1. Issue 2. |
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Page 48 of 51 |
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LK1/b | to | 74LS00 | pin | 5 | (your original 1MHz clock) |
LK1/c | " | " | " | 12 | (your 2MHz clock) |
LK1/a | " | " | " | 8 | (output clock) |
IC5/15 | " | " | " | 1 & 2 | (clock select line) |
(i.e. IC5 pin 15) |
Re-install the FDC card into your system and reconnect the drive cabling. Power up and boot up in your normal disk operating system. Everything should work as before, if not check the voltage level on IC5 pin 15 which should be low. If this is ok then check that the two clock lines are not swapped. I had no problems, everything worked first time when I booted up the disk system.
Modifying existing software should be quite straight forward. Changes only need to be made whenever commands that (potentially) move the disk drive’s head are issued to the WD1797 disk controller chip. I include details of 2 versions of software, one where primitive disk routines communicate directly with the WD1797 FDC chip and secondly where the routines communicate indirectly via a single call (i.e. SYS users).
Firstly, for routines that send commands to FDC directly, listing 1 shows the suggested alterations (in lower case) to the existing code. The existing code is presented in a hypothetical form, and you may have to alter it slightly in light of your own circumstances. The ‘FDCBUSY’ subroutine call may in fact be a jump to some common code shared by ‘HOME:’, ‘SEEK:’ and maybe other routines as well. In this case just append the source of the ‘stepslow:’ at the end for your ‘FDCBUSY’ routine.
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Page 48 of 51 |
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