H83714 Datasheet, PDF (225/324 Pages) Renesas Technology Corp – single-chip microcontrollers

12.3.4 Procedure for Starting Operation
The procedure for starting operation of the VFD controller/driver is given below for a case in
which digit pins FD₃ to FD₁₅ and segment pins FS₅ to FS₂₃ are used. It is assumed that data has
already been written to the VFD display RAM area.
• Select the digit/key-scan time and dimmer resolution with bit FLMO of the VFD digit control
register (VFDR), and select the digit waveform with bits DM2 to DM0. Clear bits DR3 to
DR0 to 0000, making pins FD₀ to FD₁₅ operational.
• Set the VFLAG bit of the VFD segment control register (VFSR) to 1, making the selected
pins valid as VFD pins. Set bit KSE to enable or disable the key scan interval. Set bits SR4
to SR0 to 11011, making pins FS₀ to FS₂₃ operational.
• Set bits DBR3 to DBR0 in the digit beginning register (DBR) to 0011, designating pin FD₃ as
the first digit pin and pin FS₅ as the first segment pin. Set bit DISP to 1, turning the display
on, and set bit VFDE to 1, starting VFD controller/driver operation.
12.4 Interrupts
When the key scan interval starts, bit IRRKS in interrupt request register 3 (IRR3) is set to 1.
These VFD interrupt requests can be enabled or disabled by means of bit IENKS of interrupt
enable register 3 (IENR3). For further details, see 3.2.2, Interrupts.
12.5 Occurrence of Flicker when VFD Registers are Rewritten
The VFD controller/driver is initialized whenever one of its registers (VFDR, VFSR, DBR) is
rewritten. If this initialization takes place while a digit is being displayed, the contents displayed
just prior to initialization will in some cases remain as an after-image in other digits. (This
depends in part on the performance of the vacuum fluorescent display, but a momentary glow may
be visible.) Frequent rewriting of the registers can make these after-images bright enough to
appear as a false display. This problem can be avoided by employing the following programming
sequence when VFD controller/driver registers are rewritten.
Step
Description
1.
DISP = 0
2.
VFLAG = 0
3.
Rewrite register (FLMO, DM0 to DM3, etc.)
4.
Wait for at least T_digit (display time of one digit). (Execute other routines.) If
the wait time is too long, the entire display may flicker. If the key scan feature
is activated, this wait time does not have to be specially programmed.
5.
VFLAG = 1
6.
DISP = 1
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