ST10F276Z5 datasheet(232/239 Pages) STMICROELECTRONICS

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Known limitations

ST10F276Z5

232/239

24.1.4

Spurious BREQ pulse in slave mode during external bus arbitration

phase

Description

Sporadic bus errors may occur when the device operates as a slave and the HOLD signal is

used for external bus arbitration.

After the slave has been granted the bus, it deactivates sporadically BREQ signal for a short

time, even though its access to the bus has not been completed. The master then starts

accessing the bus, thus causing a bus conflict between master and slave.

Workaround

To avoid producing any spurious BREQ pulse during slave external bus arbitrations, it is

necessary to ensure that the time between the HLDA assertion (Bus Acknowledge from

Master device) and the following HOLD falling edge (Bus Request from Master) is longer

than three clock cycles.

This can be achieved by delaying the HOLD signal with an RC circuit (see Figure 72).

Figure 72.

Connecting an ST10 in slave mode

24.1.5

Executing PWRDN instructions

Description

The Power-down mode is not entered and the PWRDN instruction is ignored in the following

cases:

●

The PWRDN instruction is executed while NMI is high (PWDCFG bit of the SYSCON

●

The PWRDN instruction is executed while at least one of the Port 2 pins used to exit

from Power-down mode (PWDCFG bit of the SYSCON register is set) is at the active

level.

BREQ

HLDA

HOLD

BREQ (P6.7)

HLDA (P6.6)

HOLD (P6.5)

Master

ST10 in Slave mode

VSS

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