Production Data

WM8255

w

PD, Rev 4.7, August 2013

24

-

In this mode of operation, setting the duty cycle to zero is an invalid state. The RGB switches

should be used to switch off the LED current.

This method will have no effect on colour mode performance.

BLANKING DISABLE CODE SET

Address

Data

Comment

0x01

0xA3

This will put the part into test configuration mode. Any address will now point to

the extended page reconfiguration register

0x24

0x1C

This will:

-- force the LED IDAC control state machine to stay on at all time

- force the value to be held in LEDIDACR to be loaded into the LED current DAC

0x01

0x23

This will take the part back into normal operating mode.

Notes:

1. If this COMPLETE SEQUENCE of operation is not carried out TOGETHER the part may go into an unsupported mode

To finish a mono mode scan with blanking period disabled and perform another operation, the part needs to get into a know state. Two

options are available for a complete reset of the device or a reset of the LED sequence controller:

Option 1: WM8255 global reset from blanking period disable

Address

Data

Comment

0x04

0x00

This will reset the WM8255 into its default condition. The part should now be fully

reconfigured into the user configuration.

Option 2: WM8255 LED sequence controller reset from blanking period disable

Address

Data

Comment

0x2F

0x00

This will reset LED sequence controller WM8255. All configuration data will be held.

Table 3 Blanking Period Disable

With reference to Figure 17 for current steering,

1.

The appropriate RGB matrix switch is closed allowing the LED current DAC current to flow in the

LED

2.

The first step to switch off the LED current is to close the shunt current path switch

3.

The LED is switched off by opening the RGB switch matrix.

4.

To switch on the LED, first the shunt current path switch is closed and the cycle repeats.

A make before break switch sequence is used when the LED is switched on or off. As a result the

LED current DAC always has a path to flow and never changes value.