| 摘要 |
<p>PURPOSE:To protect a head against runaway of CPU and to protect peripheral parts against burning by monitoring the head drive pulse width of a thermal head and stopping the head forcibly when the monitored pulse width exceeds a set value. CONSTITUTION:Print data are held in a latch 2, under control of a CPU 1, and head drive pulses (a) are applied through a head drive pulse width monitoring circuit 5 onto a head driver 3. The head driver 3 drives a thermal head 4 to print a character or a figure. The head drive pulses (a) are fed to an inverter 6, one output therefrom is fed through an integrator 9 and an inverter 7 to a NAND gate 8 while the other output therefrom is fed directly to the NAND gate 8. Upon reception of the head drive pulse (a), the integrator 9 starts charging operation and when the driving time is lengthened due to runaway of the CPU, the inverter 7 operates to turn the head driver 3 OFF through a reset output (c) and to reset the CPU thus stopping abnormal operation of printer.</p> |
