Data Sheet

AD7656/AD7657/AD7658

Rev. D | Page 13 of 32

Pin No.

Mnemonic

Description

7

DB8/DOUT A

Data Bit 8/Serial Data Output A. When SER/PAR = 0, this pin acts as a three-state parallel digital

output pin. When SER/PAR = 1 and SEL A = 1, this pin takes on its DOUT A function and outputs

serial conversion data.

6

DB9/DOUT B

Data Bit 9/Serial Data Output B. When SER/PAR = 0, this pin acts as a three-state parallel digital

output pin. When SER/PAR = 1 and SEL B = 1, this pin takes on its DOUT B function and outputs

serial conversion data. This configures the serial interface to have two DOUT output lines.

5

DB10/DOUT C

Data Bit 10/Serial Data Output C. When SER/PAR = 0, this pin acts as a three-state parallel digital

output pin. When SER/PAR = 1 and SEL C = 1, this pin takes on its DOUT C function and outputs

serial conversion data. This configures the serial interface to have three DOUT output lines.

4

DB11

Data Bit 11/Digital Ground. When SER/PAR = 0, this pin acts as a three-state parallel digital output

pin. When SER/PAR = 1, this pin should be tied to DGND.

3, 2, 64

DB12, DB13, DB15

Data Bit 12, Data Bit 13, Data Bit 15. When SER/PAR = 0, these pins act as three-state parallel digital

input/output pins. When CS and RD are low, these pins are used to output the conversion result.

When CS and WR are low, these pins are used to write to the control register. When SER/PAR = 1,

these pins should be tied to DGND. For the AD7657, DB15 contains a leading zero. For the AD7658,

DB15, DB13, and DB12 contain leading zeros.

1

Data Bit 14/REFBUF Enable/Disable. When SER/PAR = 0, this pin acts as a three-state digital input/

output pin. For the AD7657/AD7658, DB14 contains a leading zero. When SER/PAR = 1, this pin can be

used to enable or disable the internal reference buffers.

28

RESET

Reset Input. When set to logic high, this pin resets the AD7656/AD7657/AD7658. The current

conversion, if any, is aborted. The internal register is set to all 0s. In hardware mode, the

AD7656/AD7657/AD7658 are configured depending on the logic levels on the hardware select pins.

In all modes, the parts should receive a RESET pulse after power-up. The reset high pulse should be

typically 100 ns wide. After the RESET pulse, the AD7656/AD7657/AD7658 needs to see a valid

CONVST pulse to initiate a conversion; this should consist of a high-to-low CONVST edge followed

by a low-to-high CONVST edge. The CONVST signal should be high during the RESET pulse.

27

RANGE

Analog Input Range Selection. Logic input. The logic level on this pin determines the input range of

the analog input channels. When this pin is Logic 1 at the falling edge of BUSY, the range for the

of BUSY. In software mode (H/S SEL = 1), the RANGE pin can be tied to DGND and the input range is

determined by the RNGA, RNGB, and RNGC bits in the control register.

31

Positive Power Supply Voltage. This is the positive supply voltage for the analog input section, and

30

Negative Power Supply Voltage. This is the negative supply voltage for the analog input section, and

24

STBY

Standby Mode Input. This pin is used to put all six on-chip ADCs into standby mode. The STBY pin is

high for normal operation and low for standby operation.

62

H/S SEL

Hardware/Software Select Input. Logic input. When H/S SEL = 0, the AD7656/AD7657/AD7658

operate in hardware select mode, and the ADC pairs to be simultaneously sampled are selected

by the CONVST pins. When H/S SEL = 1, the ADC pairs to be sampled simultaneously are selected by

writing to the control register. In serial mode, CONVST A is used to initiate conversions on the

selected ADC pairs.

29

W/B

Word/Byte Input. When this pin is logic low, data can be transferred to and from the AD7656/AD7657/

AD7658 using the parallel data lines DB[15:0]. When this pin is logic high, byte mode is enabled. In this

mode, data is transferred using data lines DB[15:8] and DB[7] takes on its HBEN function. To obtain the

16-bit conversion result, 2-byte reads are required. In serial mode, this pin should be tied to DGND.