HP250 curiosity

Tony Duell ard at p850ug1.demon.co.uk
Fri Dec 7 17:53:55 CST 2007

> I was going through some of my old literature and stumbled upon a 
> discussion of the HP250 architecture.  One statement made was that it 
> was impossible for the customer to write his own binary executables 
> on this system.  The idea being that the customer would program 
> everything in HP BASIC, I imagine.
> Out of curiosity, was this restriction ever relaxed?  How many people 

Qute a number of HP machines could not be programmed in their native 
machine code. HP Technical BASIC did not inclode PEEK and POKE, for 

In the case of the 9830, there was no way to get user machine code into 
memory. You could load it from tape (but you couldn't write a machine 
code tape file from the machine), you could run it from ROM.I suppose 
some users maight have fiund ways to interface standard EPROMs to the 
machine or write the tapes (it was a standard BMS format) on something else.

In the case of the HP41 calculator, it was physcially impossible to run 
machine code from the machine's internal RAM. The processor was a pseudo 
harvard architecture, RAM was organised in 56 bit 'registers' connected 
to the SPU DATA line, ROM was in 10 bit words connected to the ISA line. 
Some hackers found a way round this, making ROM emulator boxes (normally 
called MLDL (Machine Language Development Lab) units). 

I haev no idea whcih restriction applies to the HP250. IIRC it uses the 
BPC processor hybrid (as in the HP9825), and I belive all ROM and RAM is 
in the same address space on that chip. So presumably if you can get the 
machine code into memoery and find some what to get the CPU to jump to 
it, it will run.

> have one of these in their collection?

I wish...


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