AMC7891

SBAS518A

– AUGUST 2011 – REVISED DECEMBER 2011

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GENERAL PURPOSE INPUT/OUTPUT PINS

The AMC7891 has twelve GPIO pins. Each GPIO provides a bidirectional, digital I/O signal. These pins can

receive an input or produce an output as configured by the GPIO_config register.

To configure the GPIOxx pin as an output, the corresponding ioxx_io bit needs to be set to

‘1’. The GPIOxx is an

output driver with a pull to the value of the corresponding ioxx_out bit in register GPIO_out.

To set the GPIOxx pin as an input, the corresponding ioxx_io bit has to be cleared to

‘0’. In this mode the

GPIOxx pin is in high-impedance state and the read value is stored in the corresponding ioutxx_in bit in register

GPIO_in. When set as an input, writes to the GPIO_out register do not affect the GPIO values.

After a power-on or reset event, all the GPIO pins are set as inputs and, hence in high-impedance state.

POWER-UP SEQUENCE

After all supplies are established, serial communication with the AMC7891 is valid only after a 200

µs power-up

reset delay. Following this, a software reset should be issued to ensure proper operation of the AMC7891. A

software reset is issued by writing the value

‘0x6600’ to reset[15:0] in register AMC_reset. Communication to the

AMC7891 is re-established after a 200

µS delay from the reset operation (measured from the rising edge of CS

establishing the end of the reset command frame).

At power-up or after a software-reset command all registers are set to the default values (see Table 6). The

default state of all analog blocks is off as determined by the default value of the AMC_power register.

For the device to work properly, AVDD must power up before applying any inputs to the GPIO pins. In addition, if

using an external ADC reference AVDD must power up before the external reference voltage is applied to the

REF pin.

The following power-up sequence is recommended for the AMC7891.

1. No input should be applied to the GPIO pins. Also, if using an external ADC reference, it should not be

applied to the REF pin.

2. Supply all voltages (AVDD, GPIOVDD and SPIVDD). If possible, it is recommended to apply IOVDD before

AVDD. However, the supplies can be powered up simultaneously or in any order with no detrimental effect to

the device.

3. After AVDD has been applied there is a 200 µs power-up reset delay. No serial communication should be

attempted during this time.

4. Issue a software-reset command by writing the value

‘0x6600’ to reset[15:0] in register AMC_reset.

5. Wait at least 200

µs from the rising edge of CS to complete the software-reset.

6. Program the registers according to the desired mode of operation.

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© 2011, Texas Instruments Incorporated

Product Folder Link(s): AMC7891