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参数资料
| 型号： | ST7PLITEUS5U3TR |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 8-BIT, FLASH, 8 MHz, MICROCONTROLLER, DSO8 |
| 封装： | LEAD FREE, DFN-8 |
| 文件页数： | 45/108页 |
| 文件大小： | 1957K |
| 代理商： | ST7PLITEUS5U3TR |
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9 I/O PORTS
9.1 INTRODUCTION
The I/O port offers different functional modes:
– transfer of data through digital inputs and outputs
and for specific pins:
– external interrupt generation
– alternate signal input/output for the on-chip pe-
ripherals.
An I/O port contains up to 6 pins. Each pin (except
PA3/RESET) can be programmed independently
as digital input (with or without interrupt genera-
tion) or digital output.
9.2 FUNCTIONAL DESCRIPTION
Each port has 2 main registers:
– Data Register (DR)
– Data Direction Register (DDR)
and one optional register:
– Option Register (OR)
Each I/O pin may be programmed using the corre-
sponding register bits in the DDR and OR regis-
ters: bit X corresponding to pin X of the port. The
same correspondence is used for the DR register.
The following description takes into account the
OR register, (for specific ports which do not pro-
vide this register refer to the I/O Port Implementa-
tion section). The generic I/O block diagram is
shown in Figure 28
9.2.1 Input Modes
The input configuration is selected by clearing the
corresponding DDR register bit.
In this case, reading the DR register returns the
digital value applied to the external I/O pin.
Different input modes can be selected by software
through the OR register.
Notes:
1. Writing the DR register modifies the latch value
but does not affect the pin status.
2. PA3 cannot be configured as input.
9.2.1.1 External interrupt function
When an I/O is configured as Input with Interrupt,
an event on this I/O can generate an external inter-
rupt request to the CPU.
Each pin can independently generate an interrupt
request. The interrupt sensitivity is independently
programmable using the sensitivity bits in the
EICR register.
Each external interrupt vector is linked to a dedi-
cated group of I/O port pins (see pinout description
and interrupt section). If several I/O interrupt pins
on the same interrupt vector are selected simulta-
neously, they are logically combined. For this rea-
son if one of the interrupt pins is tied low, it may
mask the others.
External interrupts are hardware interrupts. Fetch-
ing the corresponding interrupt vector automatical-
ly clears the request latch. Changing the sensitivity
of a particular external interrupt clears this pending
interrupt. This can be used to clear unwanted
pending interrupts.
Spurious interrupts
When enabling/disabling an external interrupt by
setting/resetting the related OR register bit, a spu-
rious interrupt is generated if the pin level is low
and its edge sensitivity includes falling/rising edge.
This is due to the edge detector input which is
switched to '1' when the external interrupt is disa-
bled by the OR register.
To avoid this unwanted interrupt, a "safe" edge
sensitivity (rising edge for enabling and falling
edge for disabling) has to be selected before
changing the OR register bit and configuring the
appropriate sensitivity again.
Caution: In case a pin level change occurs during
these operations (asynchronous signal input), as
interrupts are generated according to the current
sensitivity, it is advised to disable all interrupts be-
fore and to reenable them after the complete pre-
vious sequence in order to avoid an external inter-
rupt occurring on the unwanted edge.
This corresponds to the following steps:
1. To enable an external interrupt:
– set the interrupt mask with the SIM instruction
(in cases where a pin level change could oc-
cur)
– select rising edge
– enable the external interrupt through the OR
register
– select the desired sensitivity if different from
rising edge
– reset the interrupt mask with the RIM instruc-
tion (in cases where a pin level change could
occur)
2. To disable an external interrupt:
– set the interrupt mask with the SIM instruction
SIM (in cases where a pin level change could
1
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