User manual

Rev. 1.00, 05/04, page 304 of 544
Bit Bit Name
Initial
Value R/W Description
4 ICDRE 0 R Transmit Data Write Request Flag
Indicates the ICDR (ICDRT) status in transmit mode.
0: Indicates that the data has been already written to
ICDR (ICDRT) or ICDR is initialized.
1: Indicates that data has been transferred from ICDRT
to ICDRS and is being transmitted, or the start
condition has been detected or transmission has
been complete, thus allowing the next data to be
written to.
[Setting conditions]
• When the start condition is detected from the bus
line state with I
2
C bus format or serial format.
• When data is transferred from ICDRT to ICDRS.
1. When data transmission completed while ICDRE
= 0 (at the rise of the 9th clock pulse).
2. When data is written to ICDR in transmit mode
after data transmission was completed while
ICDRE = 1.
[Clearing conditions]
• When data is written to ICDR (ICDRT).
• When the stop condition is detected with I
2
C bus
format or serial format.
• When 0 is written to the ICE bit.
• When the IIC is internally initialized using the CLR3
to CLR0 bits in DDCSWR.
Note that if the ACKE bit is set to 1 with I
2
C bus format
thus enabling acknowledge bit decision, ICDRE is not
set when data transmission is completed while the
acknowledge bit is 1.
When ICDRE is set due to the condition (2) above,
ICDRE is temporarily cleared to 0 when data is written to
ICDR (ICDRT); however, since data is transferred from
ICDRT to ICDRS immediately, ICDRE is set to 1 again.
Do not write data to ICDR when TRS = 0 because the
ICDRE flag value is invalid during the time.