st10f272z2 STMicroelectronics, st10f272z2 Datasheet - Page 133

• Manufacturer Part Number: st10f272z2
• Description: 16-bit Mcu With 256 Kbyte Flash Memory And 20 Kbyte Ram
• Manufacturer: STMicroelectronics

ST10F272Z2
24.4
Spurious BREQ pulse in slave mode during external bus
arbitration phase
Description
Sporadic bus errors may occur when external bus arbitration is used via the HOLD function
and the ST10F272Z2 is configured as a slave.
After the slave has been granted access to the bus, the slave disables the BREQ signal
sporadically for a short time, even though slave access to the bus has not been completed.
The master starts then its own bus access, generating a bus conflict between master and
slave.
Workaround
To avoid producing any spurious BREQ pulse during a slave external bus arbitration phase,
it is necessary to guarantee 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 implemented by delaying the HOLD signal with an RC circuit as shown in
3.
Figure 39. ST10 in Slave mode
Master
HOLD
HLDA
BREQ
V
SS
BREQ (P6.7)
HOLD (P6.5)
HLDA (P6.6)
ST10 in Slave mode
Known limitations
133/189
Figure