PD72042B_15 Datasheet, PDF (16/92 Pages) Renesas Technology Corp – LSI DEVICE FOR Inter Equipment BusTM (IEBusTM) PROTOCOL CONTROL

µPD72042B
(4) Control field
The control field indicates the type and direction of the next data field.
The control field consists of control bits, a parity bit, and an acknowledge bit.
The four control bits are output starting with the MSB.
Following the control bits, a parity bit is output. If even parity is detected, and the function requested by the master
unit can be performed by the slave unit, the slave unit outputs an acknowledge signal. Then, the slave unit
proceeds to the data-length field. If the slave unit cannot perform the processing requested by the master unit,
even when even parity is detected, or if odd parity is detected, the slave unit does not output an acknowledge
signal, and it enters the standby (monitor) state again.
After detecting the acknowledge signal, the master unit proceeds to the data-length field.
If an acknowledge signal is not detected, the master unit enters the standby state, terminating communication.
For broadcast, however, the master unit proceeds to the next data-length field without attempting to detect the
acknowledge signal.
Table 2-3 lists the meanings of the control bits.
(5) Data-length field
The data-length field specifies the communication data length, in bytes.
The data-length field consists of the data-length bits, a parity bit, and an acknowledge bit.
The eight data-length bits are output starting with the MSB. The data-length bits indicate the communication
data length, in bytes, as shown in Table 2-2.
Table 2-2 Values of the Data-Length Bits and Their Meanings
Data-length bit (hexadecimal)
01H
02H
:
:
FFH
00H
Transmission data length, in bytes
1
2
:
:
255
256
Remark If the data length set in the data-length bits exceeds the maximum number of transmission bytes, the
latter varying with the communication mode, more than one frame is transmitted. In the second and
subsequent frames, the data-length bits indicate the remaining communication data length, in bytes.
The operation performed for this field differs depending on whether master transmission (when bit 3 of the control
bits is 1) or master reception (when bit 3 of the control bits is 0) is performed.
1 Master transmission
The data-length bits and parity bit are output by the master unit. When the slave unit detects even parity,
the slave unit outputs an acknowledge signal, then proceeds to the data field. For broadcast,
however, the slave unit does not output an acknowledge signal.
If the slave unit detects odd parity, the slave unit does not output an acknowledge signal, regarding the
received data-length bits as being incorrect. Then, the slave unit enters the standby (monitor) state again.
At this time, the master unit also enters the standby state again, and communication terminates.
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Data Sheet S13990EJ3V0DS