Lucent Technologies MN102F75K User Manual

298

Set the I

2

C connection in the I2CSEL0 and I2CSEL1 bits of the PCNT0 register 

(x’00FF90’). Since the SCL0, SDA0, SCL1, and SDA1 pins also serve as 
general-purpose port pins, and reset to the general-purpose function, you must set 

these bits every time the program uses the I

2

C function. You must also select the 

I

2

C function in the port mode registers. For I

2

C bus connection 0, set bits 0 and 1 

of the P6MD register (x’00FFFC’). For I

2

C bus connection 1, set bits 1 and 2 of 

the P0MD register (x’00FFF0’).

Table 13-4 shows the register settings required to use either SDA0/SCL0 or 
SDA1/SCL1 alone, and figure 13-5 shows the control circuit for this pin setup.

P0MD (x’00FFF0)

1

0 (selects P01)

1 (selects SDA1)

2

0 (selects P02)

1 (selects SCL1)

P6MD (x’00FFFC’)

0

1 (selects SDA0)

0 (selects P60)

1

1 (selects SCL0)

0 (selects P61)

PCNT0 (x’00FF90’)

8

1 (enables SDA0, SCL0)

0 (disables SDA0, SCL0)

9

0 (disables SDA1, SCL1)

1 (enables SDA1, SCL1)

I

2

C

Circuit

SDA IN

SCL OUT

SCL IN

SDA OUT

SDA 0

SDA1

SCL1

SCL0

I2CSEL0

Port control register 0
x'00FF90' bit 8

I2CSEL0

Port control register 0
x'00FF90' bit 8

I2CSEL0

x'00FF90' bit 9

I2CSEL0

x'00FF90' bit 9

1: on
0: off