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hp9845: some info added for 9895

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fulivi 2017-01-27 11:43:58 +01:00
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src/devices/bus/ieee488/hp9895.cpp
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@ -2,12 +2,44 @@
// copyright-holders: F. Ulivi
/*********************************************************************
hp9895.cpp
hp9895.cpp
HP9895 floppy disk drive
HP9895 floppy disk drive
Phew, this one was tough!
This is a dual 8" floppy disk drive that interfaces through
HPIB/IEEE-488 bus. It implements the so-called "Amigo" command
set.
Its main components are:
* A Z80A CPU @ 4 MHz with 8 kB of firmware ROM and 1 kB of
static RAM
* A HP PHI chip that interfaces CPU to HPIB bus
* A disk controller implemented with a lot of discrete TTLs
* 2 MPI 8" disk drives
Data I/O with the disk is carried out through 2 shift registers,
one for data bits (@ 0x60 address) and one for clock bits (@ 0x61
address). CPU is stalled by setting WAIT/ to 0 whenever it accesses
the data register and the hw is not ready for the byte. Once
the next byte boundary is reached (the SDOK signal activates) the
CPU is released and either the data byte is read from shift register
or written into it. At the same time clock shift register is
copied into clock register when reading or viceversa when writing.
The 9895 drive can operate in 2 modes: HP/High density or IBM/low
density. This table summarizes the differences between the modes.
See also page 2-12 of service manual.
| Characteristic | HP mode | IBM mode |
|----------------+----------+-----------|
| Bit cell size | 2 µs | 4 µs |
| Modulation | MMFM | FM |
| Bit order | LS first | MS first |
| Sync bytes | 4x FF | 6x 00 |
| Formatted size | 1155 kB | 250.25 kB |
Reference manual:
HP 09895-90030, feb 81, 9895A Flexible Disc Memory Service Manual