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参数资料
| 型号： | M44C892 |
| 厂商： | ATMEL CORP |
| 元件分类： | 微控制器/微处理器 |
| 英文描述： | 4-BIT, MROM, 4 MHz, MICROCONTROLLER, PDSO20 |
| 封装： | SSO-20 |
| 文件页数： | 15/84页 |
| 文件大小： | 643K |
| 代理商： | M44C892 |
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M44C892
M44C092
Rev. A5, 14-Dec-01
22 (84)
3.2
Bidirectional Ports
With the exception of Port 1 and Port 6, all other ports (2,
4 and 5) are 4 bits wide. Port 1 and Port 6 have a data width
of 2 bits (bit 0 and bit 3). All ports may be used for data
input or output. All ports are equipped with Schmitt trig-
ger inputs and a variety of mask options for open drain,
open source, full complementary outputs, pull up and pull
down transistors. All Port Data Registers (PxDAT) are I/O
mapped to the primary address register of the respective
port address and the Port Control Register (PxCR), to the
corresponding auxiliary register.
There are five different directional ports available:
Port 1
2-bit wide bidirectional ports with automatic full
bus width direction switching.
Port 2
4-bit wide bitwise-programmable I/O port.
Port 5
4-bit wide bitwise-programmable bidirectional
port with optional strong pull-ups and program-
mable interrupt logic.
Port 4
4-bit wide bitwise-programmable bidirectional
port also provides the I/O interface to Timer 2,
SSI, voltage monitor input and external interrupt
input.
Port 6
2-bit wide bitwise-programmable bidirectional
port also provides the I/O interface to Timer 3
and external interrupt input.
3.2.1
Bidirectional Port 1
In Port 1 the data direction register is not independently
software programmable, the direction of the complete
port
being
switched
automatically when an I/O
instruction occurs (see figure 22). The port is switched to
output mode via an OUT instruction and to input via an
IN instruction. The data written to a port will be stored
into the output data latches and appears immediately at
the port pin following the OUT instruction. After RESET
all output latches are set to ’1’ and the port is switched to
input mode. An IN instruction reads the condition of the
associated pins.
Note:
Care must be taken when switching the bidirectional port
from output to input. The capacitive pin loading at this
port in conjunction with the high resistance pull-ups may
cause the CPU to read the contents of the output data
register rather than the external input state. To avoid this,
one should use either of the following programming
techniques:
Use two IN-instructions and DROP the first data
nibble. The first IN switches the port from output
to input and the DROP removes the first invalid
nibble. The second IN reads the valid pin state.
Use an OUT-instruction followed by an IN–
instruction.
Via
the
OUT-instruction,
the
capacitive load is charged or discharged depend-
ing
on the optional pull-up / pull-down
configuration. Write a ”1” for pins with pull-up
resistors and a ”0” for pins with pull-down
resistors.
OUT
IN
Reset
I/O Bus
D
R
S
Q
NQ
R
Master reset
P1DATy
(Data out)
(Direction)
BP1y
VDD
*
Switched
*
Switched
*
*) Mask options
VDD
Static
pull-up
Static
pull-down
pull-up
pull–down
Figure 22. Bidirectional Port 1
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