PCA9901_1

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 01 — 3 December 2009

10 of 27

NXP Semiconductors

PCA9901

One wire single LED driver

8.8 Time-out

The time-out circuitry allows the PCA9901 to be safely set back to the Shutdown mode

when a communication problem occurs between the host controller and the PCA9901.

8.8.1 CTRL LOW too long after receiving a TRAINING START command

The PCA9901 is waiting for the first LED ON timing.

1. Once the TRAINING START command has been decoded (end of the 1.5 ms

window), a time-out counter starts counting as long as CTRL stays LOW.

2. The time-out counter counts until it reaches the maximum allowed ON value. The

maximum allowed ON time is greater than or equal to 255 ms.

Remark: If CTRL goes HIGH before reaching the maximum counter value, the

time-out counter is reset and the PCA9901 starts counting the LED ON timing or

decoding the command that has been issued.

3. If the maximum time-out value is reached, the training sequence is automatically

terminated and the PCA9901 goes to Shutdown mode.

Remark: When the time-out occurs and the PCA9901 goes to Shutdown mode, the

registers are still programmed with zeroes.

8.8.2 CTRL HIGH too long during the training sequence

The PCA9901 is counting the ON timing and reaches the counter maximum value (0xFF).

If CTRL does not go LOW when reaching the max value:

1. The PCA9901 switches off the LEDOUT pin.

2. Maximum ON count is stored in the corresponding ON register.

3. A time-out counter starts counting until it reaches the maximum allowed OFF value.

The maximum allowed OFF time is greater than or equal to 5.11 seconds.

4. When the maximum time-out counter value is reached, maximum OFF count is stored

in the corresponding OFF register.

Remark: If CTRL goes LOW before reaching the maximum counter value, the

time-out counter is reset and the PCA9901 starts counting the LED OFF timing.

5. If the maximum time-out value is reached, the training sequence is automatically

terminated and the PCA9901 goes to Shutdown mode.

8.8.3 CTRL LOW too long during the training sequence

The PCA9901 is counting the OFF timing and reaches the counter maximum value

(0xFF). If CTRL does not go HIGH when reaching the maximum value:

1. Maximum OFF count is stored in the corresponding OFF register.

2. A time-out counter starts counting until it reaches the maximum allowed OFF value.

The maximum allowed OFF time is greater than or equal to 5.11 seconds.

3. When the maximum time-out counter value is reached, the training sequence is

automatically terminated and the PCA9901 goes to Shutdown mode.

Remark: If CTRL goes HIGH before reaching the maximum counter value, the

time-out counter is reset and the PCA9901 starts counting the LED ON timing or

decoding the command that has been issued.