18 Feb
2012
18 Feb
'12
3:17 p.m.
I was just thinking that when we dump a ROM/PROM contents we get a
binary file out. In order to understand that binary file we need to
know some metadata about the data, such as:
I am not sure what the point of this would be, To understand a PROM dump
you often need to know a lot more than that, in fact you often need
schematics, (and maybe PAL equations, etc) for the device it goes in.
And if you have that, most of these questions are answered.
- what is the organization of the chip/data?
Is it 2048x1 bit or is it 256x8 bits?
For PROms with word lengths <=8 biMs (which covers just about all
'classic' ones, it's normal to put one word pe byte, in the low bits of
the bute and pack with 0s's. So a 256*4 dump would be 256 bytes long, the
high nybble of each byte of the dump woul;d be zero.
- is it a character generator table for a terminal?
If it is, that doesn't tell you everything about it Not all character
generators are simple bit-maps. In particular, many character cells on
older terminals.dispalys were 7 bits wide, but normal 8-bit EPROMs were
used for the chaacter generator. Thie extra bit of the EPROM (often the
MSB) was used i na variety of ways, 2 common ones being to extend the
last bit sent to the screen into the inter-character gap (so that line
drawing chartacters join up), or to signal that this row of the pattern
should be shifter by half a dot width to get smoother diagonals (som HPs
did that certainly.
- is it microcode for a CPU?
Again, you'd need to know a lot about the CPU architecture to make sense
of it if it was. Porbably a schematic would be a good start... And the
schematic will show the size/organisation of the PROM.
- is it code for a commercial microcontroller/microprocessor?
if so, which chip is it for? (8086, 8051, 6809, etc.)
That would eb a good start, but again you need to know things like the
I.O structure to fully understnad the code in tha lot of cases.
- what part number information is on the chip package?
Does that matter? Many manfacturers used a variet of makes of PROMs at
differnt times, based on cost/availability/... I don;'t think it matters
that the PROM dump came from an MMI PROM and that the machine you're
fixing has an equicalent (for reading at least) National Semiconducator
PROM in it.
- if there is a printed label on the packge, what does it say?
(i.e. version number label on an EPROM)
- who performed the dump of the data?
what is their contact information?
Why on earth odes that matter?
It seems to me that this small amount of metadata could easily be
Actually, in a lot of cases for older machine, the metadata would be
several times the size of the PROM dump. 32*8 (thats' 32 bytes, not
Kbytes) PROMs were common, used for address decoders, microcode funciton
decordes, state machine tables, etc. I susepct specifying the machine it
came out of, the lcoation in the circuit, the basic fuction, and the
organisation, would take a lot more than 32 bytes.
-tony