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PCA9550 Datasheet(PDF) 4 Page - NXP Semiconductors |
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PCA9550 Datasheet(HTML) 4 Page - NXP Semiconductors |
4 / 17 page Philips Semiconductors Product data PCA9550 2-bit I2C LED driver with programmable blink rates 2003 May 02 4 DEVICE ADDRESSING Following a START condition the bus master must output the address of the slave it is accessing. The address of the PCA9550 is shown in Figure 3. To conserve power, no internal pull-up resistor is incorporated on the hardware selectable address pin and it must be pulled HIGH or LOW. 11 0 0 0 0 A0 SLAVE ADDRESS SW00928 FIXED HARDWARE SELECTABLE R/W Figure 3. Slave address The last bit of the address byte defines the operation to be performed. When set to logic 1 a read is selected while a logic 0 selects a write operation. CONTROL REGISTER Following the successful acknowledgement of the slave address, the bus master will send a byte to the PCA9550 which will be stored in the Control Register. 0 0 AI B2 B1 B0 0 SW01034 0 AUTO-INCREMENT FLAG REGISTER ADDRESS RESET STATE: 00h Figure 4. Control register CONTROL REGISTER DEFINITION B2 B1 B0 REGISTER NAME TYPE REGISTER FUNCTION 0 0 0 INPUT READ INPUT REGISTER 0 0 1 PSC0 READ/ WRITE FREQUENCY PRESCALER 0 0 1 0 PWM0 READ/ WRITE PWM REGISTER 0 0 1 1 PSC1 READ/ WRITE FREQUENCY PRESCALER 1 1 0 0 PWM1 READ/ WRITE PWM REGISTER 1 1 0 1 LS0 READ/ WRITE LED SELECTOR REGISTER DESCRIPTION The lowest 3 bits are used as a pointer to determine which register will be accessed. If the auto-increment flag is set, the three low order bits of the Control Register are automatically incremented after a read or write. This allows the user to program the registers sequentially. The contents of these bits will rollover to ‘000’ after the last register is accessed. When auto-increment flag is set (AI = 1) and a read sequence is initiated, the sequence must start by reading a register different from the input register (B2 B1 B0 0 0 0 0). Only the 3 least significant bits are affected by the AI flag. Unused bits must be programmed with zeroes. INPUT — INPUT REGISTER bit 7 6 5 4 3 2 1 0 default 0 0 0 0 0 0 X X The INPUT register reflects the state of the device pins. Writes to this register will be acknowledged but will have no effect. PSC0 — FREQUENCY PRESCALER 0 bit 7 6 5 4 3 2 1 0 default 1 1 1 1 1 1 1 1 PSC0 is used to program the period of the PWM output. The period of BLINK0 + (PSC0 ) 1) 38 PWM0 — PWM REGISTER 0 bit 7 6 5 4 3 2 1 0 default 1 0 0 0 0 0 0 0 The PWM0 register determines the duty cycle of BLINK0. The outputs are LOW (LED off) when the count is less than the value in PWM0 and HIGH when it is greater. If PWM0 is programmed with 00h, then the PWM0 output is always LOW. The duty cycle of BLINK0 is: 256 – PWM0 256 PSC1 — FREQUENCY PRESCALER 1 bit 7 6 5 4 3 2 1 0 default 1 1 1 1 1 1 1 1 PSC1 is used to program the period of PWM output. The period of BLINK1 + (PSC1 ) 1) 38 PWM1 — PWM REGISTER 1 bit 7 6 5 4 3 2 1 0 default 1 0 0 0 0 0 0 0 The PWM1 register determines the duty cycle of BLINK1. The outputs are LOW (LED off) when the count is less than the value in PWM1 and HIGH when it is greater. If PWM1 is programmed with 00h, then the PWM1 output is always LOW. The duty cycle of BLINK1 is: 256 – PWM1 256 LS0 — LED SELECTOR LED 1 LED 0 bit 7 6 5 4 3 2 1 0 default 1 1 1 1 0 1 0 1 The LSx LED select registers determine the source of the LED data. 00 = Output is set LOW (LED on) 01 = Output is set Hi-Z (LED off - default) 10 = Output blinks at PWM0 rate 11 = Output blinks at PWM1 rate |
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