UPD784938 Datasheet, PDF (496/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 20 IEBus CONTROLLER
[Description of communication error source]
<Timing error>
Condition of occurrence: If the high-/low-level width of the communication bit exceeds or falls below a rated
value.
Remark:
Each rated value is set by the bit processing block and is monitored by the internal
8-bit timer. If a timing error occurs, an interrupt is issued.
<Parity error>
Condition of occurrence:
Remark:
Limitations:
If the generated parity and received parity do not coincide in each field while the unit
serves as a receive unit.
During individual communication, if a parity error occurs in other than the data field,
an interrupt is issued.
During broadcasting communication, even if a parity error occurs in the data field, an
interrupt is issued.
If a broadcasting communication request is performed and a slave request
defeated in contention occurs, no interrupt is generated even if a parity error
occurs in the data field.
<NACK reception>
Condition of occurrence:
Remark:
If NACK is received during the ACK period in the slave address, control, or telegraph
length field while the unit serves as a receive transmit unit.
If NACK is received (transmitted) in other than the data field, an interrupt is issued.
<Underrun>
Condition of occurrence:
Remark:
If the data that is to be transmitted next to the data register (DR) until ACK is received
is not written in time during data transmission.
If underrun occurs, an interrupt is issued.
<Overrun>
Condition of occurrence:
Remark:
When the unit is used as a receive unit, a data interrupt request (INTIE1), which stores
data one byte at a time in the data register (DR), is generated, and the CPU performs
DR read processing. If this read processing is late and the next data receive timing
starts, an overrun error occurs.
When the unit is used for individual communication reception, no acknowledge is
returned during the ACK period of the next data. Through this, the transmission unit
performs retransmission of the data. Therefore, the communication count register
(CCR) is decremented, but the success count register (SCR) is not decremented.
When the unit is used for broadcast communication reception, a communication error
interrupt request (INTIE2) occurs, and reception is stopped. At this time, DR is not
updated. Moreover, no INTIE1 is generated, and the DR reception status flag (bit
1 of the timer mode control register (SSR)) is set (to 1) and maintained. The overrun
status is canceled using the data reception timing following DR read.
496
Preliminary User’s Manual U13987EJ1V0UM00