HP262x keyboard voltage

[Rik Bos]

According to the museum site (www.hpmuseum.net) the electronics of the HP125
and HP120 are mostly the same. 
It seems the housing and screen size are the biggest difference between
these machines. 
I didn't checked my HP125 out just tested and fixed (bad video ram 4116) it
when I got it, and ran some progs CP/M on it.
I like the looks of it, not the internal design solutions.
Playing with a 200 or 300 series is more fun.

-Rik

> -----Oorspronkelijk bericht-----
> Van: cctalk-bounces at classiccmp.org 
> [mailto:cctalk-bounces at classiccmp.org] Namens Tony Duell
> Verzonden: maandag 6 april 2009 20:39
> Aan: cctalk at classiccmp.org
> Onderwerp: Re: HP262x keyboard voltage
> 
> > 
> > It's a strange desing using a terminal to interface with a 
> CP/M computer.
> 
> A bit like an H89/Z90 :-)
> 
> I was looking at the HP120 design at a lower level. There 
> are, as you said, 2 processors. They communciate by a simple 
> 1-byte parallel interface, and AFAIK you can't run user code 
> on the 'terminal' processor.
> 
> The terminal side uses that strange video chip I asked about 
> a couple of weeks back. It interrupts the terminal Z80 on 
> every character line, the Z80 then loads the start address of 
> that line into the processor and the apporpriate attributes 
> into a latch. The video chip then does DMA and fetches 80 
> byes from memory into an octal 80-bit shift register chip. 
> This is sent to the character generator and then to the CRT. 
> 
> Note I mentioned that attirbutes are loaded per line. On each 
> line, a character is either 'normal' or has the atributes 
> applies (some combination of underlined, blinking, 
> intensified, etc). Note you can't have some underlined (but 
> normal brightness) and some intesified (but not
> underlined) characters on the same line. There's also no 
> grpahics capability. This would be reasonable if memory was 
> limited, but that terminal processor has 16K RAM and 32K ROM 
> hung off it. The serial ports are on the terminal processor bus
> 
> Now the user processor has 64K RAM, and an 8K ROM that can be 
> paged out. 
> It also has the HPIB itnerface on its bus. And from what I 
> can tell, the HPIB interface is polled, there are no interrupts. 
> 
> I mentioend the lack of any form of graphics. I also can't 
> find any way for a program on the user processor to configure 
> the serial ports. You do that from the setup menu, which is 
> code running on the terminal processor. 
> 
> And while there's an exteded CP/M BIOS function to send a 
> byte to an HPIB device, there doesn't seem to be one to read 
> from an HPIB device. Yes, OK, since the HPIB controller is in 
> the user processor I/O space it's possible to get round that, 
> but since the disk drives are hung off that HPIB port, you 
> could easily get the thing into a state where it couldn't 
> access the disks, or worse managed to corrupt them.
> 
> I find the sales pitch for this series of machines (on 
> hpmusuem.net) to be worring due to the number of 
> misconceptions and downright lies it spreads about comepeting 
> machines. I would have though an HP machine should be able to 
> stand on its own merits (most, IMHO, can!).
> 
> -tony
>