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Here are the photocopies of the data sheet for the Western Digital 1770 chip.
If you refer to page 45 you will see under the column ARCHITECTURE the description of the track, sector, data, status, and command registers.
In the Zebra controller, these are accessed by the following port assignments:
- Command/Status register Port CO
- Track register C1
- Sector register C2
- Data register C3
The Data Request signal (DRQ) described on page 47 can be tested by bit 7 of port 2F.
One quick and easy way to see some of these in action is to use DDTZ.COM on the FORMAT.COM.
I hope your continuation of the FDD Express gets off to a good start. I’ll be in contact with you soon by mail with a write up of some of the things I am working on.
I now have 3.5″ DSDD drives running on my old model controller and I’ve been studying the 80 track format to see how it differs from the 40 track SSDD. I was able to find some of the formatting routine in the TOS code. My preliminary review shows that it first formats the first side of the disk with 80 tracks, 16 sectors per track, and 256 bytes per sector. This gives 80 tracks with 4K storage per track for a total capacity of 320K. It then selects side 2 of the disk and repeats the same operation to give another 320K storage capacity. The operating system is written to the first 4 tracks and the fifth track is reserved for the directory,
This means that of side 1, 20K is reserved for TOS and the directory leaving 300K for file storage on side 1. This plus the 320K on side 2 gives a total of 620K file storage capacity.
I’m testing some of the utilities I wrote which were published in Time Designs or which I uploaded to the Club Forum Library 14 of Compuserve and find that they do work on the 80 track disks. I need to investigate how TOS automatically switches from side 1 to side 2. My goal is to write a 80 track version of FORMAT.COM for the CP/M mode and to adjust those areas of CBIOS so the high density format can be used under CP/M.