HT45R37V Holtek Semiconductor Inc., HT45R37V Datasheet - Page 23

• Manufacturer Part Number: HT45R37V
• Description: C/r-f Type 8-bit Otp Mcu
• Manufacturer: Holtek Semiconductor Inc.

VFD Driver
The device includes a VFD driver function to drive VFD
panel high voltage filaments and buzzer. The
microcontroller communicates serially with the VFD
driver transmitting the display data into a 24-bit shift reg-
ister within the driver. This VFD driver converts the shift
register into VFD panel driving signals and makes the
necessary voltage level shifting. The microcontroller will
only transmit data to the VFD driver, no data is transmit-
ted from the VFD driver to the microcontroller.
VFD Interface
A five line interface exists between the microcontroller
and the VFD driver as shown in the diagram.
Data transmission between the microcontroller and the
VFD interface is conducted via a three line interface us-
ing the CLK, DATA and STROBE lines. As data commu-
nication is only one way the microcontroller I/O pins
must bet setup as outputs.
The buzzer control input BZI will be transformed into a
complementary pair of outputs BZO and BZO by a con-
verter in the VFD driver. These complementary buzzer
outputs will also be level shifted to a higher voltage by
the converter. The VFD driver filament control input, F1,
will also be shifted to a high voltage output called F1O,
that can be used to switch the filaments on and off.
Rev. 1.00
VFD Display Control Timing Diagram
VFD Driver
23
24-bit Shift Register/Latch
Data transmitted from the microcontroller is transmitted
serially and will be first written into a 24-bit shift register
located within the VFD driver. These 24-bits are used to
control the VFD panel segments, VFD0~VFD15, and
grid, VFD16~VFD23, lines. The control method is as fol-
lows:
Use the DATA and CLK lines to shift data into the
internal 24-bit shift register. Data is clocked into the
shift-register on the positive clock edge. This data cor-
responds to the desired VFD0~VFD23 output display
data. The VFD outputs will only change if the
STROBE line is high. If the STROBE line is low, only
the shift register data will be modified and the VFD
outputs will remain the same.
Use the STROBE line to latch the shift-register data
to the VFD0~VFD23 outputs. When the STROBE line
is high, the shift register data will be latched to the
VFD lines. Note that the STROBE line is level and not
edge triggered.
October 20, 2009
HT45R37V