MarsMan2020
Experienced Member
I picked up a couple of really nice Hitachi 1.2MB 5.25" drives at VCF this year - cast housings, black faceplates, originally used in IBM mainframes to load firmware updates.
I was hoping to use these to replace the Micropolis drives in my Vector MZ - but I can't seem to find any option to jumper the drives for 300 RPM operation. They appear to be 360 RPM only.
I am wondering if I fed my Micropolis FDC board a 360/300*2 MHz = 2.4 MHz clock, and adjusted the center frequency of the VCO in the PLL circuit to 360/300*1 MHz = 1.2 MHz - would the board work with a 360 RPM drive? Pretty much everything on the board is 7400 series logic, I would expect that it would handle a 20% speed difference OK. Might have to adjust the one-shot durations up/down to match as well.
The one big problem I would see would be some of the timing requirements with the driver software on the Z80, which needs to write preambles/data/postambles with the correct timing in response to flags from the FDC controller when it sees the sector pulses. Still, I'd be surprised if 20% caused a big difference there.
Any thoughts? Is this worth trying? Or should I try to trace out the controller boards on the floppies and find a way to get them to 300RPM instead?
(Note: I fully understand that using these drives will not be disk-compatible with my Micropolis drives due to being 96 TPI vs 100 TPI - but due to the Micropolis drives being such a pain, I only have a couple of disks anyway. I'd use my Vector MZ a lot more if I had more reliable drives.)
I was hoping to use these to replace the Micropolis drives in my Vector MZ - but I can't seem to find any option to jumper the drives for 300 RPM operation. They appear to be 360 RPM only.
I am wondering if I fed my Micropolis FDC board a 360/300*2 MHz = 2.4 MHz clock, and adjusted the center frequency of the VCO in the PLL circuit to 360/300*1 MHz = 1.2 MHz - would the board work with a 360 RPM drive? Pretty much everything on the board is 7400 series logic, I would expect that it would handle a 20% speed difference OK. Might have to adjust the one-shot durations up/down to match as well.
The one big problem I would see would be some of the timing requirements with the driver software on the Z80, which needs to write preambles/data/postambles with the correct timing in response to flags from the FDC controller when it sees the sector pulses. Still, I'd be surprised if 20% caused a big difference there.
Any thoughts? Is this worth trying? Or should I try to trace out the controller boards on the floppies and find a way to get them to 300RPM instead?
(Note: I fully understand that using these drives will not be disk-compatible with my Micropolis drives due to being 96 TPI vs 100 TPI - but due to the Micropolis drives being such a pain, I only have a couple of disks anyway. I'd use my Vector MZ a lot more if I had more reliable drives.)