big bucks for a Tek computer on eBay

[Philip Belben]

Ah, yes.  The Tek 4050 series - my favourite computers!  I have a search 
on eBay that's supposed to notify me when anything like that is listed, 
but I haven't had much time to read e-mails recently, so I probably 
missed it.

Al Kossow wrote:
>  > apparently 6800 based. O woe is me. 322$ + 90$
> 
> ~$400 isn't 'big bucks'

Agreed.  Years ago, a 4052 was thrown out at work.  In those days they 
were enlightened enough to ask for bids from employees before they stuck 
it in the skip (dumpster), and I bid 100 pounds to be sure of getting 
it.  I exhibited it and talked about it at the VCF in ?1998.

I also have service manuals.  Very useful, since the PSU has blown up 
twice since I got it.  The service manuals (one called "Technical Data" 
and one called "Parts List and Schematics") cost over 100 pounds each, 
*not including* 3-ring binders (which aren't that easy to get in the 
UK!), but they were worth it.

> The original 4051 used a 6800,
> 4052s simulate a 6800 with 2901s
> and are MUCH faster.

Well, lets see.

The 4052 microcode emulates a 6800 without any decimal arithmetic 
facility, but includes a couple of memory management instructions to 
give it 128K of address space.  You set bit 16 separately for 
instruction ("fetch") space and data space.  A nice feature is that 
changes to "fetch" space don't take effect until the next jump instruction.

The microcode is clocked at 25MHz, giving an equivalent clock speed of 
5MHz for the 6800 (which usually doesn't even make it to a megahertz iirc)

A further increase in speed is provided by the 16 bit data path with 
separate address buses for the two bytes, allowing it to fetch a whole 
word at a time even if the address isn't on a word boundary.  This 
knocks at least a cycle off most instructions.

The 4054 is like the 4052 but with extra graphics features: a 19 inch 
screen, 4096*4096 addressable locations, some thumbwheels as a pointing 
device, dashed lines.  It may even have had rotatable text.

The 4052A (which was just sold on eBay) and 4054A are like the 4052 and 
4054, but with a GPIB controller chip.  This frees the CPU (and ROM) of 
some of the burden of GPIB handling, and the free ROM space is used to 
provide some limited dynamic graphics - things that can move around the 
screen and not stick to the "storage" bit of it: a few vectors on the 
4052A, a couple of dozen on the 4054A I think.  I don't have the A 
upgrade, alas...

I experimented at one stage with getting the 4052 to talk to a Commodore 
disk drive.  It works, but the 4052 has an annoying habit of asserting 
IFC at the least convenient moment (such as, when it clears everything 
prior to loading a program).  I think it needs a MUPET!

Philip.