Star Micronics TSP200 Manual

next previous

– 18 –

PRINCIPLES OF OPERATION

Fig. 2-7 Timing Chart

2-2-4. Head current control

Heat buildup in the thermal printhead can cause print quality to degrade. To maintain uniform quality, the printer varies

the energizing time (time that STROBE remains LOW) in accordance with the head temperature.

The print head’s surface temperature is calculated based on the resistance value of the attached thermistor, and energizing

time is controlled accordingly.

2-2-5. Head burnout protection

Misoperation of the CPU may cause head current to remain on too long, resulting in burn damage to the elements unless

current is shut off by other means. The printer therefore includes a burnout protection circuit that automatically forces

current off at some fixed time tw following current startup. Control is implemented through the head’s BEO terminal,

which is active on HIGH; setting the terminal LOW forces current off regardless of the STROBE state.

Fig. 2-8 Head Burnout Protection Circuit

24V

CLOCK

LATCH

COMMON

STB1

STB2

STB3

HD ON

+5V

tw=(C

EXT

) (R

EXT

)

IC1

CPU

EXT

B BEOQ

IC6

CN6