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VSC056

Data Sheet

Revision 4.1

January 2008

3.2.76 8Ch: Pulse Train Control 90 (PTC90)

This register, along with the PTC91 register, provides a user-programmable LED flashing pulse train that

defines the 0.25 Hz flash rate (selectable in the bit control registers) at power on. The user can adjust the

pulse duration, pulse train length, and the on/off time to derive a specific visual indication. The PTC90

contains two bits of pulse-width programmability, two bits of pulse train length programmability, and the

remaining four bits of the programmable pulse train.

As an example, the pulse train can be used to develop a visual heartbeat indication by programming the

PTC90 register with a 45h and the PTC91 register with a 01h. This combination develops a pulse train

with two blinks followed by a gap with the on times of the LED equal to 166.67 ms.

If the default values of this register or the PTC91 register are modified, and synchronization to other LED

flash rates is desired, the SYNC# pin must be enabled. To enable the SYNC# pin, tie the SYNCEN pin to

VDD, connect an external 10 kΩ pull-up resistor to the SYNC# pin, and place the proper synchronization

value in bits 3:0 of the Clock Select Control register. For information on the Clock Select Control register,

see “FDh: Clock Select Control (CSC),” page 111.

The following table shows the bit assignments for the Pulse Train Control 90 registers.

PTC90

Address:

8Ch

Reset Value:

0011_1111b

Description

Pulse Train Control 90

Bit

Bit Label

Access

Description

7:0

PT7-0

R/W

Pulse Train

These eight bits are the first bits shifted out from 0 to 7 and define the on/off

time for the 0.25 Hz (FS2-FS0 = 001b in the selected bit control register) flash

rate.

1: defines LED on time.

0: defines LED off time.

VSC056 Datasheet(PDF) 83 Page - Maxim Integrated Products