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PCA9555AHF Datasheet(PDF) 11 Page - NXP Semiconductors |
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PCA9555AHF Datasheet(HTML) 11 Page - NXP Semiconductors |
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11 / 39 page  PCA9555A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved. Product data sheet Rev. 1 — 11 September 2012 11 of 39 NXP Semiconductors PCA9555A Low-voltage 16-bit I2C-bus I/O port with interrupt and weak pull-up 7.2 Reading the port registers In order to read data from the PCA9555A, the bus master must first send the PCA9555A address with the least significant bit set to a logic 0 (see Figure 4 “PCA9555A device address”). The command byte is sent after the address and determines which register will be accessed. After a restart, the device address is sent again, but this time the least significant bit is set to a logic 1. Data from the register defined by the command byte is sent by the PCA9555A (see Figure 9, Figure 10 and Figure 11). Data is clocked into the register on the falling edge of the acknowledge clock pulse. After the first byte is read, additional bytes may be read but the data now reflects the information in the other register in the pair. For example, if Input Port 1 is read, the next byte read is Input Port 0. There is no limit on the number of data bytes received in one read transmission, but on the final byte received the bus master must not acknowledge the data. After a subsequent restart, the command byte contains the value of the next register to be read in the pair. For example, if Input Port 1 was read last before the restart, the register that is read after the restart is the Input Port 0. Remark: Transfer can be stopped at any time by a STOP condition. Fig 9. Read from register A S START condition R/W acknowledge from slave 002aah346 A acknowledge from slave SDA A P acknowledge from master DATA (first byte) slave address STOP condition S (repeated) START condition (cont.) (cont.) 1 0 0 A2 A1 A0 1 A 0 R/W acknowledge from slave slave address at this moment master-transmitter becomes master-receiver and slave-receiver becomes slave-transmitter NA no acknowledge from master 1 0 0 A2 A1 A0 0 0 data from lower or upper byte of register LSB MSB DATA (last byte) data from upper or lower byte of register LSB MSB 0/1 0 0 0/1 0/1 0/1 0/1 0 command byte |
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