Key Contacts Matrix And Solder Points; 1 ] Key Contacts Matrix - Brother PT-2300 Service Manual

3.2.4

Key Contacts Matrix and Solder Points

[ 1 ] Key contacts matrix
On the main PCB is a key contacts matrix that is a set of 50 carbon-printed key contact patterns
except for the "On/Off (
nodes.
The rubber key pad is made of high-impedance silicon rubber. As shown in Fig. 3.2-3, each key
on the rubber key pad 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.
Fig. 3.2-4 shows a key scan timing scheme and KO0-KO6 scanning pulse outputs.
The CPU scans the key contacts matrix every 14 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.
)" key. (Refer to Fig. 3.2-5.) Each contact pattern has a pair of electric
Fig. 3.2-3 Structure of a Key
Fig. 3.2-4 Key Scan Timing Scheme and Scanning Pulse Outputs
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