HT45R35V Holtek Semiconductor Inc., HT45R35V Datasheet - Page 24

• Manufacturer Part Number: HT45R35V
• Description: C/r To F Type 8-bit Otp Mcu
• Manufacturer: Holtek Semiconductor Inc.

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.
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:
Rev. 1.00
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
VFD Display Control Timing Diagram
VFD Driver
24
The accompanying table shows the 24-bit shift regis-
ter/latch function truth table:
Note:
Programming Considerations
After power on all the I/O lines will be automatically
setup as inputs. However as lines PB3~PB7 are used to
drive the VFD and buzzer interface, they should be
setup as outputs after power is applied to the device. Al-
lowing the VFD interface control lines to be setup as in-
puts will create an incorrect VFD display and buzzer
operation. It is advised that the configuration options se-
lect pull-high resistors to be connected to these lines to
keep the lines at a fixed high level when power is initially
applied and until the lines can be setup as outputs.
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.
Clock
X means don t care
VFDn means VFD1~VFD23
Strobe
0
1
1
1
Data
X
0
1
1
No change No change
No change No change
VFD0
0
1
January 15, 2009
HT45R35V
VFDn-1
VFDn-1
VFDn