I wrote two little C++ code snippets which can be used to access
the Latch16Bit board and devices attached to it. The code is not the
most performant one but it is easy-to-read and has a clean design.
The code is divided into two files, one for the low level line printer
port access (which can be shared among several higher-level interfaces)
and one for the Latch16Bit board level. The latter allows you to set
channels (non)transparent, switch outputs to High-Z or set data on the
data bus. Higher-level functions allow you read/write one channel while
keeping a different channel transparent (by temporarily latching the
transparent channel).
You may need the following files. These files were written by me and
available under the GNU GPL. They are from December 2003
(for users of earlier versions it is strongly recommended to update).
The source builds natively on Linux ix86 using gcc. Please note that you
must pass (at least) -O to gcc when compiling
the code (because inline macros like outb(2) won't get
substituted otherwise).
There are no detailed build instructions here because this is not a program
of its own and I can assume that you are familiar with the compile-and-link
procedure anyway and would be bored reading it.
Note, however, that you may need to configure the source and your computer.
You must have a bidirectional port (maybe check the BIOS) and you must know
the port's base address (e.g. 0x378).
Also note that it may be necessary to insert wait states (especially
on faster computers). Use CONTROL_OUTPORT_DELAY
and DATA_OUTPORT_DELAY in lpportio.h
for this purpose.
Using a P1 with 100MHz, I do not need wait states for data output
(>2us pulse width) but I need a 35-cycle loop for the control output
because the control lines seem to be pull-only (with some pull-up resistor
to +5V) which means that they cannot react faster than some microseconds!
Note also that you need a bidirectional parallel port.
I switched mine to "bidirectional" mode in the BIOS
and it works. Don't know about other computers.
There is no extra documentation available here.
Please check the lengthy comments in the header files (and the actual
source code, if needed) if you want to know how to use the code.
Feel free to have a look at
the Atmel programmer to see some
code actually using this API.
