HP-41CL Update module using HP-IL
This module for the HP-41CL contains some instructions that allow reading and writing 16-bit images to and from HP-IL mass storage devices.
In addition there is an RPN program that is used to control the process which is better documented in the hp-41cl_update project.
Traditionally, a ROM page in the HP-41 is 4K large. As it uses 10-bit
memory, there is a choice of compressing it when storing it to a byte oriented
file system. However, the
.rom file format is an uncompressed memory page,
and uses 2 bytes for each memory location. Thus, it will normally have the
6 upper bits set to 0.
In the HP-41CL, the physical memory system is actually 16-bit wide, though it only exposes 10-bit to the Nut CPU (logical memory). These previosuly unused bits now have a meaning as they are used to control the speed of the faster NEWT CPU to pace it in timing loops. Additionally, some special HP-41CL modules make use of the extra bits for data purposes.
As a result, there is now a need to pass 16-bit ROM images to the HP-41CL. The read and write instructions provided in this module makes it possible to transfer such (uncompressed) 16-bit ROM images between the physical memory of the HP-41CL and HP-IL mass storage.
Read and write instructions
RDROM16 instruction reads a physical memory page from HP-IL mass
storage to HP-41CL RAM memory.
WRROM16 instruction writes a physical memory page to HP-IL mass storage.
Both instructions expects a filename in the Alpha register and the physical address page in X.
The physical address page is a 3-digit binary number, it can be specified either as a BCD number or as a binary number (non normalized number, NNN).
To specify page
801 (hex), you can enter it as an ordinary number
If the address page contains hex digits above 9, for example
need to specify it as an NNN. This can be done in two ways, either enter the
address in Alpha register and use the traditional
CODE instruction, or
load the Ladybug module, enable hex mode and type in the hex number in X.
To save page 810 (hex), enter filename in Alpha register and type:
810 in X XEQ WRROM16
To load page 800 (hex), enter filename in alpha register and type:
800 in X XEQ RDROM16
Details on the page numbers
In case you wonder about the X register input, recall how a floating point number is represented in the HP-41
S MMMMMMMMMM SXX
S is the sign,
MMMMMMMMMM is the mantissa and
SXX is the
exponent with its sign.
If the mantissa is non-zero, the address is obtained by taking the first
3 digits of
MMMMMMMMMM and treating that as a binary page address.
As these are BCD encoded digits, it means that if you enter
800, it will
get treated the hex number
800, in fact you can actually just type
it will appear at the first position and the rest of
MMMMMMMMMM will be 0.
If you enter
800003, it will still take the first 3 digits and treat that
If the mantissa is 0,
WRROM16 expects that
a binary page address (12 bits).
To enter a binary page address you need to use
CODE, which is a common
instruction from the good old days of the HP-41. It allows converting a hex
number in the Alpha register to a binary (non-normalized) number in X.
If you are using the PPC ROM, you can do as follows:
ALPHA 8AF ALPHA ; type in the page number XEQ HN ; hex to NNN (works the same as `CODE`) ALPHA filename ALPHA XEQ RDROM16 ; read from file
An alternative way is to use the Ladybug module which uses binary integers as its native numbers. This means that you can just enter the 3 digit hex number in X from the keyboard:
WSIZE 56 ; set word size to 56 bits ; (any word size 12 or wider will work) ALPHA filename ALPHA 8AF_ H ; type the page number as `8AF` XEQ RDROM16 ; read from file
There is a wide range of error messages that can result from using these instructions, some are explained below.
NONEXISTENT is given if there is no HP-IL module attached
DATA ERROR is given if the address is outside allowed range (the allowed range is
SIZE ERR is given by
RDROM16if the file size is not 8K bytes.