23 Jan
2023
23 Jan
'23
11:21 a.m.
On 1/23/2023 12:11 PM, Jim Brain via cctalk wrote:
Thank you for clearing up the CoCo 3, I never had one. I know the
MC6887 could address and handle the refresh for 96K.
On 1/23/2023 11:53 AM, Mike Katz via cctalk wrote:
I don't recall if that was the CoCo 2 or CoCo 3 but the system could
handle 1.8MHz (with a MC68B08E CPU). The memory had to be 2MHz to
handle the alternate cycling.
The straight MC6809 (non E version) used a more forgiving quadrature
clock but could not be alternate cycled.
The 6883 SAM was the "glue" that provided all of the timing and
address decoding for the entire system. To reduce flicker the 6847
and 6809E memory accesses were alternate cycled. This means that
they used opposite edges of the Phase 1 clock to access memory.
However, this meant running the system at .8949 MHz. The SAM had the
ability to run the CPU at twice that speed but this resulted in the
video being disabled.
Are you sure about that? The system could be sped up, which involved
not refreshing DRAM, but all of the support ICs and the DRAMs are
1MHz, so I don't think 2MHz was possible on the CoCo, at least.
There are many programs and peripherals available for the Color
Computer. The floppy disk system used 5 1/4" diskettes and could run
operating systems like Flex, Star DOS and OS/9 Level 1. I don't
recall if OS/9 Level II was ported to the Color Computer.
Yes, it was, but only for the CC3, which had an MMU (don't shoot the
messenger, that's what Radio Shack called it) and 128kB of DRAM, with
an option to expand to 512kB.
The source has been open sourced and extended as "NitrOS9", and
there's a current "Ease of Use" edition that can be loaded from a
CoCoSDC and also has 6309 extensions for faster operation.
OS9 Level II was designed by Motorola and Microware and made full use of
the capabilities of the 6809 architecture. With simple Dynamic Address
Translation 1MB of extended address space was available.
I used to run OS9 Level II on a Gimix 6809 system and then on a
Hazelwood 6809 System. Running on Dual 5 1/4" floppies, Dual 8"
floppies, a 5 1/4" hard disk drive and a syquest removable 5 1/4" drive.
I wrote the OS/9 Level II drivers for the Gimix DMA Floppy Disk
Controller back in the 1980/1981 time frame.
It's too bad but those systems are long gone and now I play with my
PDP-8 😁.
I believe there was even some kind of hard disk drive interface
available, though not from Tandy IIRC.
GlensideIDE, sold in the day by the still active Glenside Color
Computer Club (GCCC) in Chicago, IL. Also, Cloud9's SuperIDE was also
sold. There was a "Burke and Burke" HDD interface that consisted of
an adapter, an ISA MFM card (as I recall), and an MFM drive
Please just google Tandy Color Computer.
Yep.
THere's a half dozen FB group, a Discord Channel, and a mailing list.
Jim