M16C65 Datasheet, PDF (637/829 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M16C/60

Under development
M16C/65 Group
Preliminary Specification
This is a preliminary specification and is subject to change.
25. Multi-Master I²C-bus Interface
25.3.5 Start Condition Overlap Protect
The I²C interface generates a start condition by setting registers S10 and S00 by a program. The bus
system must be free before setting these registers. Check whether the bus is free with the BB bit in the
S10 register by a program before setting the registers.
However, even if the bus system is checked free, other master devices may generate a start condition
before setting registers S10 and S00. In this case, when the I²C interface detects the start condition,
the BB bit becomes 1 (bus busy) and the start condition overlap protect function is performed.
The start condition overlap protect function operates as follows.
• The start condition standby state is not entered even if the S10 register is set to E0h.
• If the I²C interface is in the start condition standby state, exit the state.
• A start condition trigger is not generated even if a data is written to the S00 register by program.
• Bits MST and TRX in the S10 register are set to 0 (slave-receiver mode).
• The AL bit in the S10 register becomes 1 (arbitration lost detected).
Figure 25.10 shows Start Condition Overlap Protect Operation.
The following is an example for start condition overlap protect operation if start condition is generated by an
external device in start condition standby state
SCLMM
SDAMM
BB bit in the S10 register
Bus free
AL bit in the S10 register
Check that BB bit is 0 (bus free) by a
program
Enter the start condition standby
state by a program
Start condition set by an external device
Bus busy
Start condition overlap protect operates
Start condition standby state exited
Start condition trigger generation disabled
AL bit becomes 1
MST bit in the S10 register
TRX bit in the S10 register
1.5 fVIIC cycles
Figure 25.10 Start Condition Overlap Protect Operation
The start condition overlap protect is enabled from the falling edge of SDAMM (start condition) to the
completion of the slave address receive. If data is written to register S10 and S00 during the period, the
above operation is performed. Figure 25.11 shows Start Condition Overlap Protect Function Enable
Period.
REJ09B0484-0030 Rev.0.30 Sep 09, 2008
Page 602 of 791