modern serial terminal

[Tony Duell]

> 
> On Nov 8, 2007 12:44 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
> 
> > 1 bit (ALU width for binary operations)
> > 3 bits (Phyiscial width of user program RAM)
> > 4 bits (ALU width for BCD operations)
> > 6 bits (Logical width of user program RAM)
> > 8 bits (physiical width of user data RAM)
> > 16 bits (physical size of registers, ROM width, logical width of data RAM)
> 
> Does it have a separate ALU for binary and BCD operations, or does it
> just ignore the upper 3 bits of the BCD ALU in each stage of a binary
> operation?  If so, I'd probably call it a 4 bitter.
> 

The ALU is a pair of programmed 256 nybble ROMs. One of them handles 
binary operations and the low bit of BCD operations, the other handles 
the high 3 bits of BCD operations (that's a simplification, if you want 
to see the scheamtics, grab 'my' scheamtics for the HP9810 from 
hpmuseum.net and look at the data path board). There are a couple of 
D-types hung off said ROMs for the binary and BCD carry flags.

Actually, since the programmer-accessible registers are almost all 16 
bits long (A and B accumulaotrs, P program counter, etc) and since the 
only thing that bothers about the fact that it's a bit-serial machine is 
the microcode, it's normally classed as a 16 bit (albeit bit serial) machine.

-tony