Key Contacts Matrix - Brother PT-530 Service Manual

3.2.5

Key Contacts Matrix

[ 1 ] Key contacts matrix
On the main PCB is a key contacts matrix that is a set of 62 carbon-printed key contact patterns
except for the On/Off key. (Refer to Figure 3.2-5.) Each contact pattern has a pair of electric
nodes.
The rubber keypad is made of high-impedance silicon rubber. As shown in Figure 3.2-3, each key
on the rubber keypad consists of a key top, return spring, and carbonic silicon rubber which
functions as a switching element.
If a particular key is pressed, the carbonic silicon rubber of the key short-circuits the paired electric
nodes carbon-printed on the main PCB.
Figure 3.2-4 shows a key scan timing scheme and K00-K07 scanning pulse outputs.
The CPU scans the key contacts matrix every 16 ms. If the CPU reads the same data on an input
port four successive times, it interprets the state as the key being pressed; if the CPU reads the
same data four successive times, it interprets the state as the key being released.
Figure 3.2-3 Structure of a Key
Figure 3.2-4 Key Scan Timing Scheme and Scanning Pulse Outputs
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