Nonvolatile, Quad, 8-Bit DACs

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11

Serial Interface

The MAX5105/MAX5106 communicate with micro-

processors (µPs) through a synchronous, full-duplex 3-

wire interface (Figure 2). Data is sent MSB first and is

transmitted in one 14-bit word. A 4-wire interface adds

a line for RDY/BSY (MAX5105), indicating the status of

the nonvolatile memory. Data is transmitted and

received simultaneously.

Figure 3 shows the detailed serial interface timing. Note

that the clock should be low if it is stopped between

updates. DOUT is high impedance until a valid read

command and address is written to the device.

Serial data is clocked into the 14-bit shift register in an

MSB-first format, with the start-bit, configuration, and

address information preceding the actual DAC data.

Data is clocked in on CLK’s rising edge while CS is low.

CS must be low to enable the device. If CS is high, the

interface is disabled and DOUT remains unchanged.

CS must go low at least 100ns before the first rising

edge of the clock pulse to properly clock in the first bit.

With CS low, data is clocked into the shift register on

the rising edge of the external serial clock.

Serial Input Data Format

and Control Codes

The 14-bit serial input format, shown in Figure 4, com-

prises one start bit, two control bits (C0, C1), three

address bits (A0, A1, A2), and eight data bits (D7–D0).

The 5-bit address/control code configures the DAC as

shown in Table 2.

Nonvolatile Store Command

The nonvolatile store command loads the 8-bit DAC

data into the selected nonvolatile DAC register, or the

DAC operating states into the mute/shutdown non-

volatile register. The nonvolatile store command does

not affect the current DAC outputs or operating states.

Once the control and address bits are clocked in,

RDY/BSY (MAX5105) goes low until the nonvolatile

store operation is complete. For the MAX5106, wait the

maximum 13ms store time before writing a new word to

the device. Do not write new data to the device until

RDY/BSY (MAX5105) returns high, or the 13ms store

time (MAX5106) has elapsed. Figure 5 shows the non-

volatile store command timing diagram.

Table 2. Serial Interface Programming Commands (continued)

14-BIT SERIAL WORD

START

C1

C0

A2

A1

A0

D7–D0

FUNCTION

1

1

1

0

0

0

XXXXXXXX

Load DAC0 nonvolatile register. Contents of DAC0 nonvolatile

register are loaded into the corresponding volatile register and

OUT0 updated. D7–D0 are ignored, and all other DAC outputs

remain unchanged.

1

1

1

0

0

1

XXXXXXXX

Load DAC1 nonvolatile register. Contents of DAC1 nonvolatile

register are loaded into the corresponding volatile register and

OUT1 updated. D7–D0 are ignored, and all other DAC outputs

remain unchanged.

1

1

1

0

1

0

XXXXXXXX

Load DAC2 nonvolatile register. Contents of DAC2 nonvolatile

register are loaded into the corresponding volatile register and

OUT2 updated. D7–D0 are ignored, and all other DAC outputs

remain unchanged.

1

1

1

0

1

1

XXXXXXXX

Load DAC3 nonvolatile register. Contents of DAC3 nonvolatile

register are loaded into the corresponding volatile register and

OUT3 updated. D7–D0 are ignored, and all other DAC outputs

remain unchanged.

1

1

1

1

0

0

XXXXXXXX

Load mute/shutdown nonvolatile register. Contents of

mute/shutdown nonvolatile register are loaded into the

mute/shutdown volatile register, and all DACs are placed into their

respective mute/shutdown states. D7–D0 are ignored.