Lucent Technologies MN10285K, MN102F75K, MN102F85K, MN102H75K 5.6.4 Setting Up I2C Transmission Using Serial Interface 0

Serial Interfaces
Serial Interface Setup Examples
MN102H75K/F75K/85K/F85K LSI User Manual Panasonic Semiconductor Development Company
137
Panasonic
5.6.4 Setting Up I2C Transmission Using Serial Interface 0
This example illustrates the microcontroller as a master transmitter in the I2C
mode, using the SBO0 and SBT0 pins.
■To set up the output ports:
I2C mode requires open-drain
pins. To set this up, set the
ODASCI0 bit of PCNT0
(x’00FF90’) to 1. In addition, set
the P5PUP7 and P5PUP5 bits of
P5PUP (x’00FFB5’) to enable
pullup control of the SBO0 and
STB0.
Set the P5MD7 and P5MD5 bits of the port 5 output mode register (P5MD) to 1.
This selects the SBO0 and SBT0 pins as the output port for the I2C interface.
P5MD (example) x’00FFFA’
■To set up the I2C interface:
The parity bits serve as the ACK
signal. To output an ACK = 1 sig-
nal, select a fixed parity of 1. To
output an ACK = 0 signal, select
a fixed parity of 0. Select a parity
of none if there is no ACK signal.
Set the operating conditions in the serial control register (SC0CTR). Select ACK
= 1 output for the transfer clock (SC0PTY[2:0] = b’101’), 8-bit character length
(SCLN = 1), I2C protocol (SC0PTL = 1), I2C mode (SC0ICM = 1), and MSB-
first bit order (SC0OD = 1). Enable both transmission and reception (SC0TEN
and SC0REN = 1) and disable transmission breaks (SC0BRE = 0). Select the
timer 0 underflow rate divided by 8 as the clock source.
SC0CTR (example) x’ 00FD80’
■To set up the start sequence:
Reception must be enabled for
the circuit to detect a start
sequence.
Write a 1 to the SC0IIC bit of the SC0CTR register to signal the start sequence.
The SBO0 pin output immediately goes low. Read SC0STR to verify that the
start sequence occurred correctly (SC0IST = 1). At this point, even if another
start exists on the bus, an arbitration lost will not be detected.
■To transmit the first data byte:
1. Load the data to the serial port 0 transmit/receive buffer, which initiates data
output. The SBO0 pin begins data output to the I2C bus when the SBT0
clock signal goes low, with a 1/8 clock cycle delay.
2. After transmission, both the SBO0 and SBT0 signals stay low.
■To transmit a second data byte:
Load the data to the serial port 0 transmit/receive buffer. The sequence for the
first data byte repeats.
■To set up the stop sequence:
1. When all the data has been transmitted, set the SC0IIC bit of SC0CTR to 0.
Never perform this step during transmission.
Bit:76543 210
P5
MD7 P5 MD6 P5 MD5 P5 MD4 P5 MD3 P5 MD2 P5 MD1 P5 MD0
Setting:10100000
Bit:1514131211109876543210
SC0
TEN SC0 REN SC0 BRE SC0 I2CS SC0 PTL —SC0 OD SC0 I2CM SC0 LN SC0 PTY2 SC0 PTY1 SC0 PTY0 SC0 SB —SC0 S1 SC0 S0
Setting:1100101111010001