HD6433713 datasheet(225/324 Pages) RENESAS

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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

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

DISP = 0

VFLAG = 0

Rewrite register (FLMO, DM0 to DM3, etc.)

Wait for at least Tdigit (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.

VFLAG = 1

DISP = 1

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