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https://codeberg.org/cryu/micro-sci-a2-controller
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47 lines
2.1 KiB
Markdown
47 lines
2.1 KiB
Markdown
# Micro-SCI / Franklin Apple ][ Floppy Drive Controller
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This is a clone of the Micro-SCI / Franklin floppy drive controller.
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v0.1 is a direct clone, reverse-engineered from a Micro-SCI board. It was cross-checked with a Franklin-branded board, as well as the (belatedly discovered) official Franklin schematic (included in doc/service_and_schematics.pdf)
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v0.2 has the following enhancements over the original design:
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* the 2708 EPROM has been replaced with a more-common 2716/2732 EPROM
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* decoupling capacitors have been added
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* footprints for all capacitors and resistors have been modernized
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* firmware EPROM bank selection jumpers replaced with a DIP switch
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* obsolete MPS-U51 transistor replaced with modern equivalent
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* clearly-marked calibration test points have been added
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* ground pours used to increase operational stability
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* support for using Floppy Emu in dual-drive emulation mode with one cable
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Firmware images can be built via the Makefile in the firmware subdirectory. The build framework requires cc65.
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## EPROM bank select switches (J4)
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* 1:off 2:off - firmware "put jumpers here" splash screen (0x0300)
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* 1:off 2: on - 13-sector firmware (0x0200)
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* 1: on 2:off - 16-sector firmware (0x0100)
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* 1: on 2: on - controller test firmware (0x0000)
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## Calibration procedure
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* set J4 to on/on ("controller test firmware")
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* connect oscilloscope to TP1
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* start machine
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* execute "call 50688"
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* execute "AAW" (and immediately hit ESC)
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* adjust R1 until waveform period is 5.4 microseconds
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* connect oscilloscope to TP2
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* execute "99W" (and immediately hit ESX)
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* adjust R2 until waveform period is 3.8 microseconds
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* card is now calibrated, power off machine and set J4 to "16-sector firmware"
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## Construction notes
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* J3 can be omitted if this controller is used with a FloppyEmu
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* All discrete logic ICs (except U15, the 74LS373) can be CMOS (74ACT, 74HCT). As is unfortunately usual with the Apple ][, U15 must be LS due to timing issues.
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* if CMOS logic is used, then Q1/R6/R7 can be omitted -- the entire logic array can remain powered up at all times. Connect pads 1 and 3 on the Q1 footprint.
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