HT80C51 datasheet(71/132 Pages) ETC2

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HT80C51 User Manual

Peripheral Modules – I2C Interface (SIO1)

Handshake Solutions

Page 71 of 132

Data Transfer After Loss of Arbitration

Arbitration may be lost in the Master Transmitter and Master Receiver modes (see [Figure 17]). Loss

of arbitration is indicated by the following states in S1STA: 38H, 68H, 78H, and B0H (see [Figure 21]

and [Figure 22]).

If the STA flag in S1CON is set by the routines which service these states, then, if the bus is free again,

a START condition (state 08H) is transmitted without intervention by the CPU, and a retry of the total

serial transfer can commence.

Forced Access to the I2C Bus

In some applications, it may be possible for an uncontrolled source to cause a bus hang-up. In such

situations, the problem may be caused by interference, temporary interruption of the bus or a tempo-

rary short-circuit between SDA and SCL.

If an uncontrolled source generates a superfluous START or masks a STOP condition, then the I2C

bus stays busy indefinitely. If the STA flag is set and bus access is not obtained within a reasonable

amount of time, then a forced access to the I2C bus is possible. This is achieved by setting the STO

flag while the STA flag is still set. No STOP condition is transmitted. The SIO1 hardware behaves as if

a STOP condition was received and is able to transmit a START condition. The ST0 flag is cleared by

hardware (see [Figure 26]).

SLA

DATA

18H

RECEPTION OF THE OWN SLAVE

ADDRESS AND ONE OR MORE

DATA BYTES ALL ARE

ACKNOWLEDGED

BOTH MASTERS CONTINUE

WITH SLA TRANSMISSION

08H

28 H

OTHER MASTER SENDS REPEATED

START CONDITION EARLIER

[Figure 25] Simultaneous Repeated START Conditions from 2 Masters

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