M16C6K9 Datasheet, PDF (206/292 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

M16C/6K9 Group
MULTI-MASTER I²C-BUS Interface
Usage precautions
(1) Access to the registers of I²C-BUS interface circuit
The precaution of read/write to the control registers of I²C-BUS circuit is as follows.
•I²C data shift register (S0i : 032016, 033016, 031016)
Do not write the register during transfer. The transfer bit counter will be reset and makes data communication
incorrect.
•I²C address register (S0Di : address 032216, 033216, 031216)
After the detection of a STOP condition, RBW is reset by H/W. Do not read/write the register at the time,
because data may become undetermined. Fig.GC-22 shows the RBW bit H/W reset timing.
•I²C control register 0 (S1Di : address 032316, 033316, 031316).
After the detection of a START condition or the completion of 1 byte transfer, bit counter (bits BC0 - BC2)
is reset by H/W. Do not read/write the register at the time, because data may become undetermined.
Fig.GC-23, GC-24 show the bit counter H/W reset timing.
•I²C clock control register (S2i : address 032416, 033416, 031416)
Do not write to this register except ACKBIT during transfer. The I²C clock generator will be reset and
makes transfer incorrect.
•I²C control register 1 (S3Di : address 032616, 033616, 031616)
Write I²C system clock selection bits when I²C-BUS interface enable bit (ES0)is in disable state. By read-
ing the data reception completion interrupt enable bit (WIT), the internal WAIT flag will be read. Thus, do
not use bit manipulation (read-modify-write instruction) to access the register.
•I²C status register (S1i : address 032816, 033816, 031816)
Do not use bit manipulation (read-modify-write instruction) to access the register because all bits of this
register are changed by H/W. Do not read/write during the timing when communication mode setting bits
MST and TRX are changed by H/W. Data may become undetermined. Fig.GC-22, GC-23, and GC-24
show the change timing of MST and TRX bits by H/W.
Rev.1.00 Jun 06, 2003 page 206 of 290