ST72321B datasheet(185/187 Pages) STMICROELECTRONICS

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KNOWN LIMITATIONS (Cont’d)

15.1.4 SCI Wrong Break duration

Description

A single break character is sent by setting and re-

setting the SBK bit in the SCICR2 register. In

some cases, the break character may have a long-

er duration than expected:

- 20 bits instead of 10 bits if M=0

- 22 bits instead of 11 bits if M=1.

In the same way, as long as the SBK bit is set,

break characters are sent to the TDO pin. This

may lead to generate one break more than expect-

ed.

Occurrence

The occurrence of the problem is random and pro-

portional to the baudrate. With a transmit frequen-

19200

baud

(fCPU=8MHz and SCI-

BRR=0xC9), the wrong break duration occurrence

is around 1%.

Workaround

If this wrong duration is not compliant with the

communication protocol in the application, soft-

ware can request that an Idle line be generated

before the break character. In this case, the break

duration is always correct assuming the applica-

tion is not doing anything between the idle and the

break. This can be ensured by temporarily disa-

bling interrupts.

The exact sequence is:

- Disable interrupts

- Reset and Set TE (IDLE request)

- Set and Reset SBK (Break Request)

- Re-enable interrupts

15.1.5 16-bit Timer PWM Mode

In PWM mode, the first PWM pulse is missed after

writing the value FFFCh in the OC1R register

(OC1HR, OC1LR). It leads to either full or no PWM

during a period, depending on the OLVL1 and

OLVL2 settings.

15.1.6

TIMD

set

simultaneously

with

interrupt

If the 16-bit timer is disabled at the same time the

output compare event occurs then output compare

flag gets locked and cannot be cleared before the

timer is enabled again.

Impact on the application

If output compare interrupt is enabled, then the

output compare flag cannot be cleared in the timer

interrupt routine. Consequently the interrupt serv-

ice routine is called repeatedly.

Workaround

Disable the timer interrupt before disabling the tim-

er. Again while enabling, first enable the timer then

the timer interrupts.

Perform the following to disable the timer:

TACR1 = 0x00h; // Disable the compare interrupt

TACSR |= 0x40; // Disable the timer

Perform the following to enable the timer again:

TACSR &= ~0x40; // Enable the timer

TACR1 = 0x40; // Enable the compare interrupt

15.1.7 I2C Multimaster

In multimaster configurations, if the ST7 I2C re-

ceives a START condition from another I2C mas-

ter after the START bit is set in the I2CCR register

and before the START condition is generated by

the ST7 I2C, it may ignore the START condition

from the other I2C master. In this case, the ST7

master will receive a NACK from the other device.

On reception of the NACK, ST7 can send a re-start

and Slave address to re-initiate communication

15.1.8 Pull-up always active on PE2

The I/O port internal pull-up is always active on I/O

port E2. As a result, if PE2 is in output mode low

level, current consumption in Halt/Active Halt

mode is increased.

15.1.9 ADC accuracy 32K Flash devices

The ADC accuracy in 32K Flash Devices deviates

from table in section 12.12.3 on page 169 as fol-

lows:

Symbol

Max

Unit

|ET|

LSB

|EO|

|EG|

4.5

|ED|

|EL|

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