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PCA9548PW Datasheet(PDF) 5 Page - NXP Semiconductors |
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PCA9548PW Datasheet(HTML) 5 Page - NXP Semiconductors |
5 / 16 page Philips Semiconductors Product data sheet PCA9548 8-channel I2C switch with reset 2004 Sep 30 5 DEVICE ADDRESSING Following a START condition the bus master must output the address of the slave it is accessing. The address of the PCA9548 is shown in Figure 3. To conserve power, no internal pullup resistors are incorporated on the hardware selectable address pins and they must be pulled HIGH or LOW. A1 A0 0A2 SW00915 1 1 1 R/W FIXED HARDWARE SELECTABLE Figure 3. Slave address The last bit of the slave address 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 PCA9548, which will be stored in the control register. If multiple bytes are received by the PCA9548, it will save the last byte received. This register can be written and read via the I2C-bus. B3 B2 B1 B0 SW00932 B7 B6 B5 B4 CHANNEL 0 CHANNEL 1 CHANNEL 2 CHANNEL 3 CHANNEL 4 CHANNEL 5 CHANNEL 6 CHANNEL 7 CHANNEL SELECTION BITS (READ/WRITE) 65 4 2 1 0 73 Figure 4. Control register CONTROL REGISTER DEFINITION One or several SCx/SDx downstream pair, or channel, is selected by the contents of the control register. This register is written after the PCA9548 has been addressed. The 2 LSBs of the control byte are used to determine which channel is to be selected. When a channel is selected, the channel will become active after a stop condition has been placed on the I2C-bus. This ensures that all SCx/SDx lines will be in a HIGH state when the channel is made active, so that no false conditions are generated at the time of connection. Table 1. Control Register; Write — Channel Selection/ Read — Channel Status B7 B6 B5 B4 B3 B2 B1 B0 COMMAND X X X X X X X 0 Channel 0 disabled X X X X X X X 1 Channel 0 enabled X X X X X X 0 X Channel 1 disabled X X X X X X 1 X Channel 1 enabled X X X X X 0 X X Channel 2 disabled X X X X X 1 X X Channel 2 enabled X X X X 0 X X X Channel 3 disabled X X X X 1 X X X Channel 3 enabled X X X 0 X X X X Channel 4 disabled X X X 1 X X X X Channel 4 enabled X X 0 X X X X X Channel 5 disabled X X 1 X X X X X Channel 5 enabled X 0 X X X X X X Channel 6 disabled X 1 X X X X X X Channel 6 enabled 0 X X X X X X X Channel 7 disabled 1 X X X X X X X Channel 7 enabled 0 0 0 0 0 0 0 0 No channel selected; power-up/reset default state NOTE: Several channels can be enabled at the same time. Ex: B7 = 0, B6 = 1, B5 = 0, B4 = 0, B3 = 1, B2 = 1, B1 = 0, B0 = 0, means that channels 7, 5, 4, 1, and 0 are disabled and channels 6, 3, and 2 are enabled. Care should be taken not to exceed the maximum bus capacitance. RESET INPUT The RESET input is an active-LOW signal which may be used to recover from a bus fault condition. By asserting this signal LOW for a minimum of tWL, the PCA9548 will reset its registers and I2C state machine and will deselect all channels. The RESET input must be connected to VDD through a pull-up resistor. POWER-ON RESET When power is applied to VDD, an internal Power On Reset holds the PCA9548 in a reset state until VDD has reached VPOR. At this point, the reset condition is released and the PCA9548 registers and I2C state machine are initialized to their default states, all zeroes causing all the channels to be deselected. |
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