P83C524 datasheet(35/76 Pages) PHILIPS

35 / 76 page

1997 Dec 15

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers

P83C524; P80C528; P83C528

13.2.1

READING OR WRITING THE S1BIT SFR

Reading or writing the S1BIT SFR starts an I2C bit I/O

sequence: some flags are cleared (SI, CLH, RBF, WBF),

clock stretching is finished and the auto-clock is started.

An auto-clock pulse is 'OR-ed' with SCO and thus will be

output only if the SCO flag has been set to 0. SCO = 1

inhibits the auto-clock start, so a dummy read or write of

S1BIT SFR can be used to finish clock stretching and clear

SI, CLH, RBF and WBF if the auto-clock is not used.

The auto-clock is an active HIGH SCL pulse that starts 28

XTAL clock periods after the SDI read or SDO write via

S1BIT. The duration of the auto-clock pulse is 100 XTAL

clock periods. If the SCL line is kept LOW by any device

that wants to hold up the bus transfer, the auto-clock

counter waits after 20 XTAL clock periods so that the

auto-clock pulse length will be at least 80 XTAL clock

periods (5

µs at fOSC = 16 MHz).

Every bit I/O should be followed by a RBF or WBF bit test.

A bit transfer has been finished successfully if after reading

a bit the RBF flag is 1 or after writing a bit the WBF flag is

1. When after reading a bit the RBF flag is still 0, the bus

status just before the S1SCS status read can be

determined as follows:

• if CLH = 0 then a bus device is still stretching the clock

• if SCI = 1 while CLH = 1 then the SCL pulse is not

finished

• if BB = 0 there has been a STOP condition.

When after writing a bit the WBF flag is still 0 and none of

the 3 status conditions mentioned for RBF are found then

a 'bus arbitration lost' condition will be the cause. This can

be determined also from the states of the received bit and

the last transmitted bit: 'arbitration loss' if SDO = 1 and

SDI = 0.

13.3

Control and Status Register for the I2C-bus (S1SCS)

Table 19 Control and Status register for the I2C-bus (address D8H)

Notes

1. SDI and SCI bits: read-modify-write operations like 'SETB bit' or 'CLR bit' access SDO and SCO for reading and

writing.

2. CLH bit: writing a logic 0 clears this bit, writing a 1 has no effect.

3. RBF and WBF bits: writing a logic 0 to CLH also clears these bits.

4. X = don't care.

76543210

READ

SDI(1)

SCI(1)

CLH(2)

RBF(3)

WBF(4)

STR

ENS

WRITE

SDO

SCO

CLH(2)

STR

ENS

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