Technical White Paper
The Unidata HSIO interface is a Unidata standard for connecting sensors, relays and displays to Neon Remote Loggers.
HSIO implementations allow up to sixteen compatible instruments to be connected to a single Unidata data logger.
Each instrument requires one 16-bit channel of bandwidth allocated to the HSIO implementation. Model 3016, 3004 and 3004M have a single bus with 8 x 16-bit channels.
Electrical Interface
The electrical interface consists of a five-wire bus system, allowing a master (datalogger) to interrogate up to 16 slaves (instruments). Signal levels are TTL compatible. They are:
SYNC
Generated by the master. It is used to indicate to the slave that a bus read is about to begin (active high).
DATA
Generated by the slave. 16 bits of data per slave. A read starts with the least significant bit of the least significant byte and each clock pulse reads the next most significant bit.
COMMON
Signal ground.
LINK
Used to connect more than one slave instrument to a bus (“daisy-chaining”). The first slave’s data line is connected to the master. The second slave’s data line is connected to the link input of the first slave. A third slave’s data line would be connected to the link input of the second slave, and so on.
CLOCK
Communications Protocol
Two data types are supported, binary and ASCII. Binary is used with the Model 6541C precision Water Level Instrument and ASCII is used with the 6526LCD.
