Table 1. control register addressing, Serial digital interface, Applications information – Rainbow Electronics MAX1400 User Manual

Page 12: Modulator data output

MAX1400

+5V, 18-Bit, Low-Power, Multichannel,
Oversampling (Sigma-Delta) ADC

______________________________________________________________________________________

Serial Digital Interface

The serial digital interface provides access to eight on-
chip registers (Figure 3). All serial-interface commands
begin with a write to the communications register
(COMM). On power-up, system reset, or interface reset,
the part expects a write to its communications register.
The COMM register access begins with a 0 start bit.
The COMM register R/W bit selects a read or write
operation, and the register select bits (RS2, RS1, RS0)
select the register to be addressed. Hold DIN high
when not writing to COMM or another register (Table 1).

The serial interface consists of five signals: CS, SCLK,
DIN, DOUT, and INT. Clock pulses on SCLK shift bits
into DIN and out of DOUT. INT provides an indication
that data is available. CS is a device chip-select input
as well as a clock polarity select input (Figure 4).

Using CS allows the SCLK, DIN, and DOUT signals to
be shared among several SPI-compatible devices.
When short on I/O pins, connect CS low and operate
the serial digital interface in CPOL = 1, CPHA = 1 mode
using SCLK, DIN, and DOUT. This 3-wire interface
mode is ideal for opto-isolated applications.
Furthermore, a microcontroller (such as a PIC16C54 or
80C51) can use a single bidirectional I/O pin for both
sending to DIN and receiving from DOUT (see

Applications Information

), because the MAX1400 drives

DOUT only during a read cycle.

Additionally, connecting the INT signal to a hardware
interrupt allows faster throughput and reliable, collision-
free data flow.

The MAX1400 features a mode where the raw modula-
tor data output is accessible. In this mode the DOUT
and INT functions are reassigned (see the

Modulator

Data Output

section).

DATA REGISTER D1–D0/CID

RS0

GLOBAL SETUP REGISTER 1

GLOBAL SETUP REGISTER 2

SPECIAL FUNCTION REGISTER

XFER FUNCTION REGISTER 1

XFER FUNCTION REGISTER 2

XFER FUNCTION REGISTER 3

DATA REGISTER D17–D10

DATA REGISTER D9–D2

COMMUNICATIONS REGISTER

RS1

RS2

DIN

DOUT

SELECT

DECODER

Figure 3. Register Summary

DIN

(DURING

WRITE)*

DOUT

(DURING

READ)*

MSB D6

INT

SCLK

(CPOL = 1)

SCLK

(CPOL = 0)

*DOUT IS HIGH IMPEDANCE DURING THE WRITE CYCLE; DIN IS IGNORED
DURING THE READ CYCLE.