Flexible IO protocol

This protocol allows a device to define a table of registers which can be read and written by the host. The registers are defined by:

• an index key
• the name of the register
• the data type: char, short, long, float
• the access mode: read-only or write-only
• an optional conversion factor to be applied by the host when exchanging data values with the device

Commands

The first byte of a packet (address) and the last (checksum) are left out in all packet descriptions/representations on this page.

Request	Response	Description
<Key>	<Byte>	Read a register value (response depending on data type of the requested register)
<Key>	<Lowbyte><Highbyte>
<Key>	<Lowbyte0><Lowbyte1><Highbyte0><Highbyte1>
<Key><Byte>	<>	Set register value (request depending on data type of the requested register)
<Key><Lowbyte><Highbyte>	<>
<Key><Lowbyte0><Lowbyte1><Highbyte0><Highbyte1>	<>
<Key><0><0><0>	<access mode, byte><data type, byte><conversion factor, float>	Read the definition of the specified register
<1><1><1><1>	<number of registers, byte>	Read the number of available registers
<Key><2><2><2>	<length of register name, byte>	Read the length of the registers name
<Key><3><3><3>	<char 0><char 1>...<char n>	Read the name of the register (not null-terminated)
<0xFF><0x00><Key 1><Key 2>…<Key n>	<0x00>: output table rejected <0x01>: output table accepted	Define the output table returned by the compound output command
<0xFF><0x01>	<max entries>	Read the maximum number of table entries supported by the compound output command
<0xFF>	depends on the output table definition	Compound output command: returns all values as defined in the output table

Available data types:

Data type	Length	Description
0	-	Unavaible register. Can be useful to remove a register without changing the keys of the remaining ones.
1	1	signed char (int8)
2	2	signed short (int16)
3	-	invalid value
4	4	signed int (int32)
5	-	Label-only register. One use case could be for the host software to display it as some kind of group label.
6	float	single accuracy floating point

Available access modes:

Access mode	Description
0	Read-only: An input value, for example the reading of an adc measurement.
1	Write-only: An output value, for example the desired speed of a motor. The host can also read it, but the device must never change it by itself.

Remarks

• Valid register keys lie in the range from 0x01 to 0xFE.
• Register values are transmitted in little endian byte order.
• When using any of the commands with a key which was not defined by the device, it will not return any answer at all.
• When trying to read a register with a data type other than 1, 2, 4 or 6, it will not return any answer at all.
• When trying to set a register which is read-only or has a data type other than 1, 2, 4 or 6, it will not return any answer at all.
• When setting a value the host can either send 1, 2 or 4 bytes for data types 1, 2 or 4. Missing data will be set to zero, exceeding data is discarded.
• If a device needs to support a register with read-write semantics (for example the speed of a motor), than this has to be modeled using two registers: a write-only register ("desired speed") and a read-only register ("measured/actual speed").