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gpibusb-firmware

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PIC firmware for GPIBUSB

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GPIBUSB Adapter Firmware
========================

This repository contains the source and hex files for the GPIBUSB firmware.

The associated PCB project can be found on GitHub at www.github.com/Galvant/gpibusb-pcb

Pre-assembled boards can be found at www.galvant.ca

Requires the CCS compiler.

About
-----

Many pieces of test & measurement equipment feature a connectivity port labelled "GPIB" which stands
for General Purpose Interface Bus. On some equipment this can also be labelled as "HPIB" after the 
company that originally invented it.

Commercial USB to GPIB adapters contain a lot of features and functionality, but are also very 
expensive ($500+ new). This is well out of price range for most hobbyists, as well as plenty of engineers
and scientists. A lot of people don't need all of the advanced GPIB communication functionality; some
are just looking to download multimeter readings or oscilloscope waveforms to their PC. This firmware
project aims to implement as much GPIB communication functionality as possible, while still remaining
accessable.

Another limitation of your typical USB to GPIB adapter is the development environment restriction
due to the required drivers. For example, these vendors only provide Linux drivers for Red 
Hat-based distributions, but these drivers do not include MATLAB bindings! Instead of having to deal
with all sorts of GPIB and VISA driver stuff, this GPIBUSB adapter presents itself to the attached PC
as a serial port, allowing a wide variety of operating systems and development environments to utilize
it. So although this means that this adapter is NOT a drop in replacement for convential ones, this
flexability is desired by many.

Installation
------------

Pre-assembled GPIBUSB adapters from www.galvant.ca already include the latest version of the firmware
installed. Updating your adapter to the latest version does not require any special hardware as
they all include the Tiny Bootloader (http://www.etc.ugal.ro/cchiculita/software/picbootloader.htm).

To update the firmware, you only require a single piece of PC software, as well as the updated hex file.
The hex file can be downloaded here: https://github.com/Galvant/gpibusb-firmware/releases. Be sure to check
which version is compatible with your hardware revision by checking the "Hardware Revisions Compatibility" 
section further down this page.

For Windows users, download the Tiny Bootloader package from 
http://www.etc.ugal.ro/cchiculita/software/tinyblddownload.htm and run "tinybldWin.exe".

For Linux users, download tinybldLin from http://tinybldlin.sourceforge.net/ . This may or may
not work on Macs as I have not tried.

With the adapter connected and the software downloaded, select the correct serial port and set 
the baud rate to 115200. Point the software to the hex file you have downloaded from here on 
github. Select "Write Flash" and immediately push the reset button the board. If everything was
successful, or if there are any error messages, a message will be displayed in the software.

Linux Users Note
----------------

For all Linux users, do note that since this adapter presents itself as a serial port, your account
will need permission to read and write to serial ports. This is done by adding your user account
to the "dialout" group. To do this, run the following command:

```Shell
$usermod -a -G dialout steven
```

Where steven is replaced with your user account name. Depending on your permissions you may need 
run this with sudo or as root.

In addition, it has been found that the software package ``modemmanager`` holds serial ports
hostage for about 30 seconds when initially connected. If you have this problem and do not require
this package it is recommended that you remove it from your system.

Communication
---------------

Baudrate: 460800

All writes to the adapter must end with a carriage return, line-feed ('\r' dec:13 or '\n' dec:10)
or some combination.

By default, all responses from the adapter will have a CR added. This can be changed with the 
``++eot_char`` command.

A small delay (0.01sec) should be added between successive commands to ensure that everything
is given time to complete.

The input buffer is about 200 bytes in size. All single continuous chunks of data from the PC should be 
strictly less than 200 bytes in length. This does not impact responces from GPIB devices to the adapter.

Command List v5
---------------

Here is the list of all commands which are used to control the adapter itself, and are not passed
onto the GPIB bus. One can avoid having to deal with most of this by using our InstrumentKit
Python library (github.com/Galvant/InstrumentKit). These commands are implemented within 
the appropriate classes to abstract them away from your code. It is HIGHLY suggested you
use the library as much as you can (and feel free to contribute classes for additional instruments!).

For all the following commands, if you omit the numeric variable the current setting will be returned.

```
++addr 1
```
Sets the GPIB address of the device you wish to communicate with. Here the target address is 1.
GPIB address range from 1 to 31. Check the device to find what its address is. When in device mode
this will set the address of the device.

```
++auto 1
```
Used to toggle automatic response reading on (1) and off (0). If set to on (default) the adapter will
automatically start reading the response from the device if your data contained a question mark (?). 
When set to off, the response will not be read and you will need to send the ``++read`` command to 
do so. This is useful for when uploading small amount of binary data to your instruments as 0x3F 
(ascii for "?") will cause the adapter to attempt to read a response. If set to on, reading will terminate
on EOI if ``++eoi 1`` is set, or will terminate on EOS charactrs if ``++eoi 0`` is set.

```
++clr
```
Sends the "Selected Device Clear" (SDC) to the currently specified GPIB address as per ```++addr```.

```
++debug 0
```
Used to toggle simple debug messages on (1) and off (0). When set to on, communicaiton timeout 
error messages are sent to the host PC containing basic details as to when and what timed-out.
This includes which data line timed-out (DAV, NDAC, NRFD), if you were waiting for it to go high or low, 
as well as if the adapter was reading or writing. Default is off.

```
++eoi 1
```
Used to toggle EOI assertion when writing on (1) and off (0). If set to on, the adapter will assert EOI
on the last byte sent over the GPIB bus. Default is on (1). Most devices will use EOI, some will give you
the option, and some will not. For those that give you the option, it is highly recommended that you
use EOI to signal end of data.

```
++eos [0|1|2|3]
```
Set the character that the adapter uses to signal end of data. EOS characters are appended to the
end of data being sent to GPIB devices and removed from the data received from GPIB devices. When
using ```++read``` reading will terminate when EOS characters are detected. There are four options
for this command: ```++eos 0``` appends CR+LF, ```++eos 1``` appends CR, ```++eos 2``` appends LF,
and ```+eos 3``` does not append anything. Default is 3.

```
++eot_enable 1
```
Used to toggle end-of-transmission (EOT) characters on (1) and off (0). When set to on, data received
from your GPIB devices will have the EOT character appended to the end when forwarded to the attached
PC. This character is specified with the ```++eot_char``` command. Default is on.

```
++eot_char 13
```
Specifies the character that will be appended to all transmissions sent from the adapter to the 
attached PC. The value is a number in the set [0,255] which is the decimal version of the desired
ASCII character. Default is 13 (CR).

```
++ifc
```
Asserts the GPIB IFC line for 150us.

```
++llo
```
Disable front panel operation of the currently addressed instrument by sending the GPIB command
byte LLO.

```
++loc
```
Enables front panel operation of the currently addressed instrument by sending the GPIB command
byte GTL.

```
++mode 1
```
Used to switch the adapter between controller mode (1) and device mode (0). Default is controller mode.

```
++read [eoi]
```
Sets the currently addressed GPIB device to talk. This is useful when ``++auto 0`` is set or if you
have an instrument that does no rely on the question mark query syntax. There are two ways to use
this command: ``++read`` will read until the EOS characters set by ``++eos`` is found, or ``++read eoi``
will read until the EOI line is asserted.

```
++read_tmo_ms 1000
```
Set the GPIB read/write timeout period in milliseconds.

```
++rst
```
Resets the GPIBUSB adapter. Any unsaved settings will be restored to the previously saved values.
Make sure to wait a few seoncds after sending this command for the adapter to fully restart.

```
++savecfg 1
```
Saves current settings to EEPROM so that they can be preserved through restarts and power cycles.
Although you can query the savecfg value with ``++savecfg``, this is only done for compatibility
reasons. The only way to save your settings to EEPROM is to send ``++savecfg 1``. The following
variables are saved: ``++mode``, ``++addr``, ``++eot_char``, ``++eot_enable``, ``++eos``, ``++eoi``,
and ``++auto``.

```
++spoll
```
Perform a GPIB serial poll on the currently specified GPIB address. In addition, you can inline
specify a different address with the syntax ``++spoll 16`` where 16 is the target GPIB address
for your serial poll.

```
++srq
```
Returns that status of the GPIB SRQ line. Returns `1` if the line is asserted or `0` if not.
If this returns `1` then that means a device on your GPIB bus is requesting service. You should
then perform serial polls via ``++spoll`` to find which device needs service.

```
++status 0
```
Sets the status byte of the adapter when in device mode. This byte is transmitted over the GPIB
bus when addressed with a serial poll. Currently, device mode will not assert SRQ no matter 
what you set the status byte to. This will be implemented in a future firmware update. Valid
values are `[0,255]`.

```
++trg
```
Perform a GPIB bus trigger on the currently specified GPIB address by sending the GPIB command
byte `GET`.

```
++ver
```
Returns the string ``Version 5.0``.

Legacy Command List
-------------------

The following commands where the primary means of interfacing with the adapter up to and including
firmware version 4. With version 5 a whole new set of commands were implemented replacing the following
ones. These ones are still included in the firmware, but there is no guarentee that they will continue
to work with newer firmwares going into the future.

```
+a:1
```
Sets the GPIB address of the device you wish to communicate with. Here the target address is 1.
GPIB address range from 1 to 31. Check the device to find what its address is.

```
+eoi:1
```
Used to toggle EOI detection on (1) and off (0). If set to on, the controller will stop reading bytes
from the device when EOI is asserted. When set to off, the controller will stop when it reads the byte
defined by the ```+eos:``` command. Default is on (1). Most devices will use EOI, some will give you
the option, and some will not. For those that give you the option, it is highly recommended that you
use EOI to signal end of data.

```
+eos:10
```
Set the character that the device uses to signal end of data. This is especially important when EOI
is off. However, some instruments will use both a termination character and use EOI. If you make sure
to set EOS even if you are using EOI data termination, the controller will suppress the last byte.
It is recommended that you disable any termination characters at the instrument and just use EOI. 
To set the termination character, put the decimal form of the character after the colon. For example, 
to set the character to 'z', you would write +eos:122

```
+read
```
Force the controller to read data from the instrument. Normally this is NOT required. When writing
commands that end with a question mark (?), the controller will automatically read the response.
However, older instruments do not include question marks at the end of query commands. In these
cases, using this command will prompt the controller to read the response data.

```
+test
```
Used to test the controller and your communication software. Controller will respond with: testing\n\r
Controller needs to be plugged into an instrument that is on (ie red LED off) for this to work.

```
+get
```
Short for “Group Execute Trigger”. This command will send the GPIB bus command to all attached
instruments. Introduced in firmware version 3.

```
+strip:0
```
Sets the number of characters to remove from the end of the instrument's response before sending 
it to the attached computer. This is useful when the instrument appends a CR as the adapter uses 
CR to terminate communication. This can prevent having to include extra serial port reads in an 
effort to clear the buffer when programming. NOTE: This command can fail if the total number of 
bytes to be sent to the computer is close to an integer multiple of 100. It is recommended that you do
not rely on this command. Introduced in firmware version 3.

```
+ver
```
Returns the firmware version. Introduced in firmware version 3. Currently returns the string `5`.

```
+autoread:1
```
Used to toggle automatic response reading on (1) and off (0). If set to on (default) the adapter will
automatically start reading the response from the device if your data contained a question mark (?). 
When set to off, the response will not be read and you will need to send the ```+read``` command to 
do so. This is useful for when uploading small amount of binary data to your instruments as 0x3F 
(ascii for "?") will cause the adapter to attempt to read a response. Introduced in firmware version 4.

```
+reset
```
Resets the microcontroller. Can be useful for when you need settings back to power-on default, or if
and instrument/device has decided it no longer wishes to listen to the GPIB bus. Introduced in firmware
version 4.

```
+debug:0
```
Used to toggle simple debug messages on (1) and off (0). When set to on, communicaiton timeout 
error messages are sent to the host PC containing basic details as to when and what timed-out.
This includes which data line timed-out (DAV, NDAC, NRFD), if you were waiting for it to go high or low, 
as well as if the adapter was reading or writing. Default is off. Introduced in firmware version 4.

Hardware Revisions Compatibility
--------------------

Here hardware revisions (left) are listed with their compatible software versions (right). The hardware
revision is marked on the silkscreen on the adapter PCB.

revB/rev2: v1 - v3

rev3 family (ie 3.1, 3.2): v4-v5

License
-------

This code is released under the AGPLv3 license. 
A copy of the license, as well as author information can be found in the LICENSE folder.

gpibusb-firmware

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