30 Jan
2001
30 Jan
'01
6:55 a.m.
From: Corda Albert J DLVA <CordaAJ(a)nswc.navy.mil>
I saw in the manual made me gag... aside from a very
small amount
of memory actually on the system bus, any add-on RAM was
accessed _serially_ (i.e. 1 bit at a time) via what TI called
a "CRU" interface (basically a high speed serial port) I
believe we can all appreciate the crippling effect on any
machine's performance when the bulk of it's memory is only
available through a 1-bit serial interface.
???? I still have 4 of them. HAving hacked one rather severely the CRU
interface was IO only. Ram was either accessed as:
128 words on the 16bit bus (pair of 6810s) this was fast ram
relative to all other.
32KW in the Expansion box, this was slower due to the word to byte
wide conversion logic (adds at least 2 waits for every access!)
Grom, byte parallel, sequential access, you wrote to a register
in the GROM to set the starting address and every byte read
would increment an internal counter. This was slow at times
being both on the byte wide bus and the higher software
maintenance. Mostly used for internal Basic and the plug in
carts.
Vram.... 16k or 4116 Dram on the video refresh bus. This was also
used as general storage for the internal BASIC and was a byte wide
access via the 9918 VTAC and also CRU IO (setting a pointer).
Horribly slow, cool graphics for the time!
I have a severely hacked one with 32KW of 61256(32kx8) and 32KW
of Eprom both 16bits wide and clocked to 4mhz... it screams. Nothing
standard and doesnt run any of the TI stuff. Nice package though.
The CRU interface for IO was actually pretty fast in practice and had
flexibility that was not available on most of the 8bitters.
BTW, I also had the technico board... a really neat
product that
never quite took off. :-(
IT's interesting that it was one of the first 16bit cpus and was not
well supported by TI at that time. Good programmers CPU.
Allison