1-10 GTECH Technical Training and Support Services
Print Head Interface
Print data is formatted by the MCF5253 and transmitted to the FPGA through a
byte serial, memory mapped I/O interface for each dot row. This interface allows
rapid transmission of data with minimal software overhead. Once the transmission
is completed, the FPGA parses, loads, and latches the data into the print head
registers using two simultaneous serial channels. Strobe timing (dot energy
control) is calculated and applied to the print head by the MCF5253. For each line
of dots printed, the head is energized twice to compensate for dot history. The
MCF5253 provides a watchdog timer that is gated in the FPGA with the strobe
signals to protect the thermal print head from overheating. All head interface lines
are buffered and resistance matched to the connecting ribbon cable.
Motor Controllers
Both the paper feed and cutter step motors are controlled by an Allegro A3988
DMOS motor driver that provides two dual-bridge, bipolar, PWM, micro-stepping
motor drivers. These drivers operate from the 24-volt supply and apply up to
1.5A/phase of output current. The drivers are micro-step capable; the controller
must provide both phase and current level information to the driver. Stepper motor
control lines are driven by FPGA outputs latched from MCF5253 processor.
The paper feed motor is set for a maximum motor current of 1A/ phase. Control
lines operate this stepper motor in ¼ step mode up to approx. 500 equivalent full
steps/sec followed by modified half step mode up to 3600 equivalent full steps/
sec.
The cutter motor circuit is also set for a maximum current level of 1A/ phase.
Control lines operate this stepper motor in modified half step mode up to approx.
1000 equivalent full steps/sec.
The stacker motor is controlled by a dedicated Allegro A3983DMOS micro-
stepping motor driver with translator. The driver is configured to operate the
stacker motor in modified half step mode at a maximum current of 500ma/phase
and is matched for stepping speeds to receive tickets passed off from the paper
feed motor.
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