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7-9
I/O PORTS
7.2.4
Bidirectional Port Considerations
This section outlines special considerations for using the pins of these ports.
Port 1
After reset, your software must configure the device to match the
external system. This is accomplished by writing appropriate config-
uration data into P1_MODE. Writing to P1_MODE not only
configures the pins but also turns off the transistor that weakly holds
the pins high (Q4 in Figure 7-1 on page 7-5). For this reason, even if
port 1 is to be used as it is configured at reset, you should still write
data into P1_MODE.
Port 2
After reset, your software must configure the device to match the
external system. This is accomplished by writing appropriate config-
uration data into P2_MODE. Writing to P2_MODE not only
configures the pins but also turns off the transistor that weakly holds
the pins high (Q4 in Figure 7-1 on page 7-5). For this reason, even if
port 2 is to be used as it is configured at reset, you should still write
data into P2_MODE.
P2.2/EXTINT0
Writing to P2_MODE.2 sets the EXTINT0 interrupt pending bit
(INT_PEND.3). After configuring the port pins, clear the interrupt
pending registers before globally enabling interrupts. See “Design
Considerations for External Interrupt Inputs” on page 7-11.
P2.4/EXTINT1
Writing to P2_MODE.4 sets the EXTINT1 interrupt pending bit
(INT_PEND.4). After configuring the port pins, clear the interrupt
pending registers before globally enabling interrupts. See “Design
Considerations for External Interrupt Inputs” on page 7-11.
P2.5/HOLD#
If P2.5 is configured as a standard I/O port pin, the device does not
recognize signals on this pin as HOLD#. Instead, the bus controller
receives an internal HOLD signal. This enables the device to access
the external bus while it is performing I/O at P2.5.
Table 7-8. Port Pin States After Reset and After Example Code Execution
Action or Code
Resulting Pin States
†
P
x
.7
P
x
.6
P
x
.5
P
x
.4
P
x
.3
P
x
.2
P
x
.1
P
x
.0
Reset
wk1
wk1
wk1
wk1
wk1
wk1
wk1
wk1
LDB P
x
_DIR, #00011111B
1
1
1
wk1
wk1
wk1
wk1
wk1
LDB P
x
_MODE, #00000000B
1
1
1
HZ1
HZ1
HZ1
HZ1
HZ1
LDB P
x
_REG, #10010011B
1
0
0
HZ1
0
0
HZ1
HZ1
†
wk1 = weakly pulled high, HZ1 = high impedance (actually a “1” with an external pull-up).
Содержание 80C196NU
Страница 1: ...8XC196NP 80C196NU Microcontroller User s Manual...
Страница 2: ...8XC196NP 80C196NU Microcontroller User s Manual August 1995 Order Number 272479 002...
Страница 18: ...1 Guide to This Manual...
Страница 19: ......
Страница 31: ......
Страница 32: ...2 Architectural Overview...
Страница 33: ......
Страница 48: ...3 Advanced Math Features...
Страница 49: ......
Страница 56: ...4 Programming Considerations...
Страница 57: ......
Страница 72: ...5 Memory Partitions...
Страница 73: ......
Страница 106: ...6 Standard and PTS Interrupts...
Страница 107: ......
Страница 144: ...7 I O Ports...
Страница 145: ......
Страница 165: ......
Страница 166: ...8 Serial I O SIO Port...
Страница 167: ......
Страница 183: ......
Страница 184: ...9 Pulse width Modulator...
Страница 185: ......
Страница 196: ...10 Event Processor Array EPA...
Страница 197: ......
Страница 225: ......
Страница 226: ...11 Minimum Hardware Considerations...
Страница 227: ......
Страница 239: ......
Страница 240: ...12 Special Operating Modes...
Страница 241: ......
Страница 255: ......
Страница 256: ...13 Interfacing with External Memory...
Страница 257: ......
Страница 303: ......
Страница 304: ...A Instruction Set Reference...
Страница 305: ......
Страница 373: ......
Страница 374: ...B Signal Descriptions...
Страница 375: ......
Страница 390: ...C Registers...
Страница 391: ......
Страница 447: ......
Страница 448: ...Glossary...
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Страница 458: ...Index...
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