III
- 4
3.2.2
CPU
The CPU (#4: MN101C28D) is an 8-bit 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 50 carbon-printed key contact
patterns (except for the On/Off key). Each contact pattern has a pair of electric nodes.
The rubber key pad is made of high-impedance silicon rubber. As shown in Figure 3.2-2,
each key on the rubber key pad consists of a key top, return 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.
Figure 3.2-3 shows a timing scheme 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 Low active for 1 ms and in high impedance while inactive. Ports P40 through
P47 act as input ports which receive key status.
The CPU scans the key contacts matrix every 10 ms. If the CPU reads the same data on
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 lockout.
Figure 3.2-2 Structure of a Key
Summary of Contents for PT 1800 - P-Touch 1800 Thermal Transfer Printer
Page 1: ...SERVICE MANUAL MODEL PT 1800 1810 ...
Page 2: ...SERVICE MANUAL MODEL PT 1800 1810 ...
Page 5: ...CHAPTER I SPECIFICATIONS ...
Page 10: ...I 4 n U S A Canada n U K Figure 1 1 2 Key Arrangement 1 ...
Page 11: ...I 5 n Germany n France Figure 1 1 2 Key Arrangement 2 ...
Page 12: ...I 6 n Belgium Figure 1 1 2 Key Arrangement 3 ...
Page 15: ...CHAPTER II MECHANISMS ...
Page 43: ...CHAPTER III ELECTRONICS ...
Page 47: ...III 3 Figure 3 2 1 Block Diagram of Main PCB ...
Page 49: ...III 5 Figure 3 2 3 Timing Scheme and Waveforms of Key Scanning by the CPU ...
Page 62: ...CHAPTER IV TROUBLESHOOTING ...
Page 65: ...IV 2 4 1 3 Troubleshooting Flows 1 Tape feeding failure ...
Page 66: ...IV 3 ...
Page 67: ...IV 4 ...
Page 68: ...IV 5 2 Printing failure ...
Page 69: ...IV 6 ...
Page 70: ...IV 7 ...
Page 71: ...IV 8 3 Powering failure Nothing appears on the LCD ...
Page 72: ...IV 9 ...
Page 73: ...IV 10 ...
Page 74: ...IV 11 4 No key entry possible ...
Page 75: ...IV 12 5 Abnormal LCD indication ...
Page 76: ...IV 13 6 Tape cassette type not identified ...
Page 77: ...APPENDICES Circuit Diagrams A Main PCB B Power Supply PCB ...