ST72321B STMICROELECTRONICS [STMicroelectronics], ST72321B Datasheet - Page 49

• Manufacturer Part Number: ST72321B
• Description: 64/44-pin 8-bit MCU with 32 to 60K Flash/ROM, ADC, five timers, SPI, SCI, I2C interface
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

I/O PORTS (Cont’d)
CAUTION: The alternate function must not be ac-
tivated as long as the pin is configured as input
with interrupt, in order to avoid generating spurious
interrupts.
Analog alternate function
When the pin is used as an ADC input, the I/O
must be configured as floating input. The analog
multiplexer (controlled by the ADC registers)
switches the analog voltage present on the select-
ed pin to the common analog rail which is connect-
ed to the ADC input.
It is recommended not to change the voltage level
or loading on any port pin while conversion is in
progress. Furthermore it is recommended not to
have clocking pins located close to a selected an-
alog pin.
WARNING: The analog input voltage level must
be within the limits stated in the absolute maxi-
mum ratings.
9.3 I/O PORT IMPLEMENTATION
The hardware implementation on each I/O port de-
pends on the settings in the DDR and OR registers
and specific feature of the I/O port such as ADC In-
put or true open drain.
Switching these I/O ports from one state to anoth-
er should be done in a sequence that prevents un-
wanted side effects. Recommended safe transi-
tions are illustrated in
transitions are potentially risky and should be
avoided, since they are likely to present unwanted
side-effects such as spurious interrupt generation.
Figure 32 on page 49.
Other
Figure 32. Interrupt I/O Port State Transitions
9.4 LOW POWER MODES
9.5 INTERRUPTS
The external interrupt event generates an interrupt
if the corresponding configuration is selected with
DDR and OR registers and the interrupt mask in
the CC register is not active (RIM instruction).
WAIT
HALT
External interrupt on
selected external
event
floating/pull-up
Mode
Interrupt Event
interrupt
INPUT
01
No effect on I/O ports. External interrupts
cause the device to exit from WAIT mode.
No effect on I/O ports. External interrupts
cause the device to exit from HALT mode.
(reset state)
floating
INPUT
00
Event
Flag
-
Description
Control
Enable
open-drain
DDRx
OUTPUT
ORx
Bit
10
XX
from
Wait
Exit
= DDR, OR
Yes
OUTPUT
push-pull
11
49/187
from
Exit
Halt