I-O Display Systems Basic I/O Product - Manual (Page 32)

Setup & Installation 2
2-15(Vol.1)
Protocol Handshake Types:
Two protocol handshake types are available, 2 pass and 4 pass.
2 Pass: The host transmits an instruction to a BASIC I/O.
If the instruction is correctly received (i.e. valid address, instruction type
and correct checksum) the BASIC I/O executes the instruction and
returns the letter “A” and a cr or, where data is to be returned, the letter
“A”, then the data, followed by a two character checksum ending with a
cr.
4 Pass: The host transmits an instruction to a BASIC I/O.
If the instruction is correctly received (i.e. valid address, but not
necessarily the correct instruction type nor checksum), the BASIC I/O
returns an “A” followed by the Echo of the instruction and does not
execute it.
If the host then transmits an E, the instruction is executed in the same
manner as the 2 pass. If the Hos transmits any other character to any unit
on the network, the instruction is disregarded.
The sequential display indicates the letter P followed by 2 or 4. BASIC I/Os are shipped in 2
pass mode; the sequential display indicates P2. The actual setting of the handshake protocol
type is detailed following network type switch.