参数资料
型号: ST72121J2T3/XXX
厂商: STMICROELECTRONICS
元件分类: 微控制器/微处理器
英文描述: 8-BIT, MROM, 8 MHz, MICROCONTROLLER, PQFP44
封装: PLASTIC, TQFP-44
文件页数: 17/87页
文件大小: 1365K
代理商: ST72121J2T3/XXX
24/87
ST72121
I/O PORTS (Cont’d)
4.1.2.4 Analog Alternate Function
When the pin is used as an ADC input the I/O must
be configured as input, floating. The analog multi-
plexer (controlled by the ADC registers) switches
the analog voltage present on the selected pin to
the common analog rail which is connected 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 Maximum
Ratings.
4.1.2.5 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 (see Figure 18) or true open drain. Switching
these I/O ports from one state to another should
be done in a sequence that prevents unwanted
side effects. Recommended safe transitions are il-
lustrated in Figure 17. Other transitions are poten-
tially risky and should be avoided, since they are
likely to present unwanted side-effects such as
spurious interrupt generation.
Figure 17. Recommended I/O State Transition Diagram
with interrupt
INPUT
OUTPUT
no interrupt
INPUT
push-pull
open-drain
OUTPUT
24
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