17 Dec
2005
17 Dec
'05
3:43 p.m.
On Sat, 17 Dec 2005, Dave Dunfield wrote:
Or is there a reason why your 8" and 5.25"
48TPI disks can't be run at the
standard PC drive A: and B: positions?
Because some on-board FDCs don't support FM. Honestly it's very nasty to
open the PC and jumper the secondary FDC to the primary address and
disable the on-board FDC and change the BIOS setup...
BTW it's not complicated at all to support a secondary FDC (shut down the
primary if it's on the same DMA), the programming is the same.
Because 4 FDDs on one controller is not a standard PC
configuration.
Does your controller use the internal drive select register of the 765?
Does it have an external hardware register like the 2-drive select
register of the PC, and if so what is the layout and will it be the same
on different 4-drive controllers. Why does your controller have two
connectors (there are four drive selects already on the cable).
It must be some kind of standard, otherwise it wouldn't be supported by
the stock DRIVER.SYS with MS-DOS. I've just checked my card: it's a
multi-I/O 16-bit ISA card with IDE, two serial, one parallel and one FDC
(it's a Motorola MCCS3201FN), the serial/parallel stuff if handled by a
SiS 82C452A. There's a jumper for the FDC to be at 3Fx or at 37x, and so
on. The only label on the card says "IFSP-2.10". It has two connectors
because it also has four motor-on signals. You know that the four drive
selects on the connector are divided into to two select and two motor-on
signal. So you need two connectors for four drives.
Just have a look at the data sheets for e.g. the DP8473 and the i82077:
they all support four(!) drives, and it's documented, and it is realized
the same way. The PLCC version of the DP8473 (the common version) has DR0
and DR1 on pins 6 and 5 (drive select 0 and 1), *and* DR2 plus DR3 on pins
45 and 43 respectively. And for the motor-on signal, MTR0 (8), MTR1 (7),
MTR2 (1) and MTR3 (52). So connecting the unused pins on a card to a
second 34 pin header gives you two more drives! The drive select and motor
on signals are available in the digital output register (DOR), bits 0 and
1 contain the binary encoded drive number (0-3), bits 4 to 7 the 1 out of 4
motor-on lines.
Now for the i82077: drive selects are on pins 58,62,64 and 67, motor-on
signals on pins 57,61,63 and 66, same register (DOR), same use.
Now for the uPD765: No good design for the PC uses the on-chip drive
selects, and there are no on-chip motor-on signals, that's why there is an
additional register (e.g. SN74174) on board that holds these signals,
therefore called the "digital output register" (see e.g. the "HP Vectra
Technical Reference Manual Vol.1" from 8/1985)
I don't think this is all that common a setup, and
most people will find
it easier to just hook up the required drive long enough to make the
images that you need. (I provide details on my site on how to set up a
nice external drive cable).
I've setup my PC to be a multi-media machine, i.e. it can handle
multiple medias from 8" down to 3.5", it has a paper tape reader, a Facit
4070 paper tape punch, QIC tape drives, SCSI, and even an external dual
5.25" floppy drive that runs CP/M internally (yes, that's right, it's the
floppy drive for the Mupid with Z80, 64kB of RAM, and a serial port to
hook it up to the PC, BTW. the format is 96tpi single-sided FM).
I do apologize for burdening you with this. However
the image file format
I'm sorry if it sounded like a complaint, it wasn't meant to be one.
Christian