Renesas rl78 User Manual

Page of 1004
 
RL78/G1A 
 
CHAPTER  12   SERIAL  ARRAY  UNIT 
R01UH0305EJ0200  Rev.2.00 
 
 
563  
Jul 04, 2013 
12.8.5  Calculating transfer rate 
The transfer rate for simplified I
2
C (IIC00, IIC01, IIC10, IIC11, IIC20, IIC21) communication can be calculated by the 
following expressions. 
 
(Transfer rate) = {Operation clock (f
MCK
) frequency of target channel} ÷ (SDRmn[15:9] + 1) ÷ 2 
 
Caution   SDRmn[15:9] must not be set to 00000000B.  Be sure to set a value of 00000001B or greater 
for SDRmn[15:9].  The duty ratio of the SCL signal output by the simplified I
2
C is 50%.  The I
2
bus specifications define that the low-level width of the SCL signal is longer than the high-
level width.  If 400 kbps (fast mode) or 1 Mbps (fast mode plus) is specified, therefore, the low-
level width of the SCL output signal becomes shorter than the value specified in the I
2
C bus 
specifications.  Make sure that the SDRmn[15:9] value satisfies the I
2
C bus specifications. 
 
Remarks 1.  The value of SDRmn[15:9] is the value of bits 15 to 9 of the SDRmn register (0000001B to 
1111111B) and therefore is 1 to 127. 
 2.  m: Unit number (m = 0, 1), n: Channel number (n = 0 to 3), mn = 00 to 03, 10, 11 
 
The operation clock (f
MCK
) is determined by serial clock select register m (SPSm) and bit 15 (CKSmn) of serial mode 
register mn (SMRmn).