4 Dec
2024
4 Dec
'24
9:51 a.m.
On Wed, Dec 4, 2024 at 5:46 PM Mike Katz <bitwiz(a)12bitsbest.com> wrote:
The story I heard is that Motorola went to Tandy asking them to use their 6809 chip.
Tandy said, ok, you design a system for us with a cost of $xxx and we will sell it.
Motorola then designed the color computer using the 6883 SAM chip which handled almost
all of the glue logic for the system. This includes address decoding, DRAM refresh,
system clock, etc.
The CoCo was made up of 3 main chips:
6809E CPU (The E used a 2 phase clock so they could alternate cycle main RAM and video
RAM)
6883 Synchronous Address Mutiplexor (took care of all of the glue logic)
6845 Graphics Controller Chip
Actually a 6847 which is a rather different device
Add RAM and a few Misc. chips and discretes and you have a CoCo!
True.
The schematic in the datasheet I pointed to also shows the ROMs and a
pair of 6821 PIAs as in the CoCo.
Great machine but no one at Tandy realized the power of the 6809. Maybe the CoCo III
came close to exploiting all that the 6809 could do.
Tandy did sell Microware OS-9, BASIC-09. Pascal and C for the CoCo.
That was a rather nice mutliuser OS. I remember at the tme I was
runing OS-9 (initially leval 1 on a 64K CoCo 2, then level 2 on a 512K
CoCo 3) and had to use MS-DOS on a computer at a company I was doing
some work for. The latter felt so primitve by comparison.
-tony