Brother P-touch PT-210E Manuel d'entretien - Page 12
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Electronics
3.2.2
CPU
The CPU (MN101C01D) is an 8bit microprocessor produced by the CMOS silicon gate
process, which integrates a 64 kilobyte ROM and a 2048 byte RAM.
3.2.3
Key Contacts Matrix
[1]
Key contacts matrix
On the main PCB is a key contacts matrix that is a set of 51 carbon-printed key contact
patterns. Each contact pattern has a pair of electrodes.
The rubber 51 key is made of high-impedance silicon rubber. As shown in Fig. 3.2-2,
each key on the rubber 51 key consists of a key top, rubber spring, and conductive
paint which functions as a switching element.
If a particular key is pressed, the conductive paint of the key short-circuits the paired
electrodes carbon-printed on the main PCB.
Fig. 3.2-3 shows a timing chart and waveforms of key scanning by the CPU. Ports P30
through P36 on the CPU produce a series of key scanning pulses. Every scanning
pulse is in low impedance for 1 ms while active and in high impedance while inactive.
Ports P40 through P47 act as input ports which receive key statuses.
The CPU scans the key contacts matrix every 10 ms. If the CPU reads the same data
at an input port two successive times, it interprets the state as the key being pressed; if
the CPU reads the same data six successive times, it interprets the state as the key
being released. The input mode of this keying system is 2-key roll-over and 3-key lock-
out.
Fig. 3.2-2 Detailed Mechanism of a key
III - 2
P-touch
SERVICE MANUAL