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poly88.cpp: Update notes (nw)

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AJR 2017-11-30 11:29:42 -05:00
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src/mame/drivers/poly88.cpp
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@ -15,14 +15,25 @@
Poly-8813 is a disk-based computer with 3 mini-floppy drives.
Booting is done by pressing the "Load" button, mounted on the
front panel near the power switch. Although user manuals are easy
to obtain, technical information and schematics are not. The bios
makes use of illegal instructions which we do not correctly emulate.
The first of these is at 0x006A (print a character routine), while
the other is at 0x0100 (an internal copy routine). The code at 0x100
can be replaced by 7E 12 13 23 03 79 B0 C2 00 01 C9, which exactly
fits into the available space. The disk format is known to be
256 bytes per sector, 10 sectors per track, 35 tracks, single sided,
for a total of 89600 bytes.
to obtain, technical information and drive controller schematics
are not. The disk format is known to be 256 bytes per sector, 10
sectors per track, 35 tracks, single sided, for a total of 89600
bytes.
The Poly-8813 BIOS makes use of undocumented instructions which we
do not currently emulate. These are at 006A (print a character
routine - ED ED 05); another is at 0100 (move memory routine -
ED ED 03); the last is at 087B (disk I/O routine - ED ED 01). The
code at 0100 can be replaced by 7E 12 13 23 03 79 B0 C2 00 01 C9,
which exactly fits into the available space. The routine at 006A is
likewise could be exactly replaced with F5 C5 D5 E5, which enters
a display routine that appears in other assembly listings but seems
to have no entry point here. Since the ED ED opcode is defined as
for CALLN in the NEC V20/V30's 8080 mode, it might be the case that
these are actually hooks patched into the original code for
emulation purposes. (There is also a slim possibility that this
opcode invokes an undocumented feature of the NEC uPD8080AF, which
at least some models of the Poly-88 are known to have used.)
****************************************************************************/