[Coco] Four floppy drives?

[Barry Nelson]

No misunderstanding. My comments apply to either DECB or OS-9 since the limitation has to do with the hardware, which I am very familiar with. As I had mentioned, I got 8 drives working as double sided, but it required a VERY special cable with circuitry including a 4 line to 16 line demultiplexer chip wired into the cable, and modifications to the OS-9 device driver. I don't know of any way of getting more than 3 DSDD drives working in ANY OS on the CoCo with some kind of hardware and software mod. The drive select lines for it just aren't there, the 4th drive select line is the same line that selects the side, so if you use it as a side select, you only have 3 drive select lines left unless you modify the hardware in some way and change the software to recognize your modified hardware.

These are the available control lines on the I/O port in the disk controller as wired and described for a standard tandy controller and cable. This is taken from the Nitros9 code. Link here: http://geneslinuxbox.net:6309/gene/nitros9/level1/modules/rb1773.asm

* Control Register Definitions
C_HALT   equ   %10000000     Halt line to CPU is active when set
C_SIDSEL equ   %01000000     Side select (0 = front side, 1 = back side)
C_DBLDNS equ   %00100000     Density (0 = single, 1 = double)
C_WPRCMP equ   %00010000     Write precompensation (0 = off, 1 = on)
C_MOTOR  equ   %00001000     Drive motor (0 = off, 1 = on)
C_DRV2   equ   %00000100     Drive 2 selected when set
C_DRV1   equ   %00000010     Drive 1 selected when set
C_DRV0   equ   %00000001     Drive 0 selected when set


On Aug 6, 2015, at 1:18 AM, coco-request at maltedmedia.com wrote:

> Date: Wed, 5 Aug 2015 11:46:35 -0700
> From: David Gettle <david17361 at gmail.com>
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Subject: Re: [Coco] Four floppy drives?
> Message-ID:
> 	<CABvSbEQ-0R6TnTirzV6HnjhqDb6VBD1wdfHpCewouftTpiLr_w at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
> 
> You misunderstood me, under DECB the 4 drives were accessed as SSDD, the
> second side of the drives were not accessed. under OS-9 all 4 drives were
> accessed as DSDD due to the OS-9 software access method, the entire drive
> under OS-9 is accessible from 1 address line.
> 
> I'm primarily an OS-9/Nitros9 user