
User’s Manual
51
4.2 Open-Drain Outputs Used for Key Scan
The Parallel Port D outputs can be individually programmed to be open drain. This is use-
ful for scanning a switch matrix, as shown in Figure 4-2. A row is driven low, then the col-
umns are scanned for a low input line, which indicates a key is closed. This is repeated for
each row. The advantage of using open-drain outputs is that if two keys in the same col-
umn are depressed, there will not be a fight between a driver driving the line high and
another driver driving it low.
Figure 4-2. Using Open-Drain Outputs for Key Scan
o.d.
o.d.
+
+
+
+
+
+
+
Содержание Rabbit 2000
Страница 2: ...Rabbit 3000 Microprocessor User s Manual 019 0108 040731 O ...
Страница 9: ...Rabbit 3000 Microprocessor ...
Страница 29: ...20 Rabbit 3000 Microprocessor ...
Страница 64: ...User s Manual 55 5 PIN ASSIGNMENTS AND FUNCTIONS ...
Страница 79: ...70 Rabbit 3000 Microprocessor ...
Страница 80: ...User s Manual 71 6 RABBIT INTERNAL I O REGISTERS ...
Страница 123: ...114 Rabbit 3000 Microprocessor ...
Страница 137: ...128 Rabbit 3000 Microprocessor ...
Страница 157: ...148 Rabbit 3000 Microprocessor ...
Страница 207: ...198 Rabbit 3000 Microprocessor ...
Страница 249: ...240 Rabbit 3000 Microprocessor ...
Страница 255: ...246 Rabbit 3000 Microprocessor ...
Страница 277: ...268 Rabbit 3000 Microprocessor ...
Страница 343: ...334 Rabbit 3000 Microprocessor ...
Страница 345: ......