Transfer Protocol - Fujitsu F2MC-16LX MB90580 Series Hardware Manual

13.4 IEBus Communication Protocol

13.4.6 Transfer protocol

The signal transmit format of the IEBus is shown as below
Field Name
Header
No. of bits
1
Start
Frame format
bit
Mode 0
Transmit
Mode 1
time
Mode 2
Note1: P: parity bit
A: acknowledge bit where A=0: ACK and A=1: NAK
Note2: The acknowledge bit is ignored in multiaddress communication.
(1) Header
The header field is consisted of start bit and multiaddress bit.
• Start bit
The start bit is a signal used to inform the other units that data transmission starts. The unit initiating the
data transmission outputs a low-level signal (start bit) for a specific time and then outputs the
multiaddress bit.
When one unit tries to output the start bit, but it found that another unit has already output a start bit,
then the unit does not output the start bit. But it waits for the end of the start bit output by the another
unit and outputs the multiaddress bit in synchronization with the output end timing of the start bit.
The units other than the one that has started transmission detect this start bit and enters the receive
status.
• Multiaddress bit
This bit indicates whether the master selects multiaddress or normal communication. When the
multiaddress bit is '0' for multiaddress communication and is '1' for normal communication. Moreover,
multiaddress communication is divided into two modes, group multiaddress and broadcasting
communication. These two modes are identified by the value of the slave address.
In multiaddress communication, since there are two or more slave units, the acknowledge bit for each
field following the master field is not returned.
If at the same time, two or more units start transmission of a communication frame, multiaddress com-
munication takes precedence over normal communication and is the winner in arbitration.
(2) Master address field
This field is outputted by the master to identify its address for other units being communicated and is
consisted of 12 bit of master address with MSB transmitting first and 1 parity bit.
If at the same time, two or more units starts transmitting the multiaddress bit of the same value, judgement
of arbitration is based on the master address field value. Everytime when the unit transmits one bit of its
unit address, it compares the data output with the data on the IEbus. If they are found to be different, the
unit lost the arbitration and then stops transmission and enters receive status.
Since the IEBus is configured as wired AND, the unit having the least master address among the units
participating in arbitration (arbitration masters) wins arbitration. After 12-bit master address is transmitted
out, only one unit remains in transmit status as the master. This master then outputs the parity bit and let
other units confirming that the transmit master address data contains no error. After that, the slave address
field is output.
Note:Even parity is used for parity check. If the total number of '1' in master address bits is
odd, the parity bit will be set as '1'.
166 Chapter 13: IE Bus
Master
Slave address
address field
1
12 12
1
Master
Slave
Multi-
address
P
address
address
bit
bits
bits
approx. 7330 µs
approx. 2090 µs
approx. 1590 µs
Control field
field
1 1 1
1 4
Telegraph
Control
P P A
A
bits
Telegraph
Data field
length field
1 1
8
8 1 1
Data
length A
P P A
bits
bits
approx. 1590 x N µs
approx. 410 x N µs
approx. 300 x N µs
MB90580 Series
8 1 1
Data
P A
bits