Fujitsu F2MC-16LX MB90580 Series Hardware Manual page 188

13.4 IEBus Communication Protocol
case, the second and following communication frames will transmit the remaining
data bytes specified in the telegraph length field.
The function of telegraph length field differs when the master is in transmit mode (bit 3 of control bits is '1')
or receive mode (bit 3 of control bits is '0') as follow:
• Master transmit mode
The telegraph length bits and parity bit are output by the master unit. If even parity is detected by the
slave, it returns the acknowledge signal. Then the master proceeds to the data field. But in multiad-
dress communication mode, the slave does not return any acknowledge signal.
If odd parity is detected, the slave judges that the telegraph length bits have not been correctly
received, and then go into standby (monitor) mode without returning acknowledge signal. At the same
time, the master also goes into standby status, and communication ends.
• Master receive mode
The slave outputs the telegraph length bits and parity bit. If even parity is detected by the master, it
returns the acknowledge signal. But if odd parity is detected, the master judges that the telegraph
length bits have not been correctly received, and goes into the standby status without returning
acknowledge signal. Then the slave also goes into standby status, and communication ends.
(6) Data field
This field is used by the master to transmit/receive data to/from the slave. This field is consisted of eight
data bits with transmitting MSB first, parity bit and acknowledge bit.
Multiaddress communication can only be performed when the master unit transmits data and the
acknowledge signal is ignored. The operations for master transmits and receives data are described as
follow:
• Master transmit mode
When the master writes data to a slave, it transmits data bits and parity bit to the slave. Then if even
parity is detected by the slave and its receive data buffer is not full, the slave returns the acknowledge
signal. If odd parity is detected or the receive buffer is full, the slave rejects accepting the corresponding
data, and does not return the acknowledge signal.
If the acknowledge is not detected by the master, it retransmits the same data until the acknowledge bit
is detected or the maximum number of transmit bytes is exceeded.
If the parity is even and the acknowledge signal is returned from the slave, the master transmits the
next available data if the maximum number of transmit bytes is not exceeded.
In multiaddress communication mode, the slave unit does not return the acknowledge signal, and the
master transmits data on a 1-byte-by-1-byte basis.
• Master receive mode
When the master reads data from the slave, the master outputs a synchronous signal corresponding to
all the read bits. Then the slave outputs the data and parity bit to the IEBus in response to the
synchronous signal output by the master. After that, the master reads these bits and confirm the parity
check.
If odd parity is detected or the master's receive buffer is full, it rejects accepting the data and does not
return the acknowledge signal. If the maximum number of transmit bytes per frame is not exceeded, the
master repeatedly reads the same data.
If even parity is detected and the master's receive buffer is not full, the master accepts the data and
returns the acknowledge signal. If the maximum number of transmit bytes per frame is not exceeded,
the master reads the next data.
(7) Parity bit
The parity bit is used to confirm that the transmit data contains no error. It is appended to master address
bits, slave address bits, control bits, telegraph length bits and data bits.
The parity is an even parity. If the number of '1' bits in the data is odd, then the parity bit is set to '1'. If the
number of '1' bits in the data is even, then the parity bit is set to '0'.
(8) Acknowledge bit
An acknowledge bit is appended to the following location to confirm whether data has been correctly
received in the normal communication mode (communication between one unit and another):
• At the end of slave address field
• At the end of control field
• At the end of telegraph length field
168 Chapter 13: IE Bus MB90580 Series