SM6451B

NIPPON PRECISION CIRCUITS INC.—7

MICROCONTROLLER INTERFACE

The SM6451B uses a 3-wire serial interface comprising MDT (data), MCK (clock) and MLEN (latch enable)

to select channels and attenuation levels for the addressed device.

Input Timing

The microcontroller data input timing is shown in figure 1.

Data is shifted into the internal shift register on the rising edge of MCK, and the attenuation value is updated on

the rising edge of MLEN. Accordingly, data on MDT should be changed on the falling edge of MCK.

Note, however, a minimum of 16 MCK input pulses are required.

Data Format

The format of microcontroller input data is shown in figure 2.

D15, D14

Don’t care.

D13, D12

Chip address bits. D13 corresponds to ADRS1 and D12 corresponds to ADRS2. The device is addressed only

when ADRS1:ADRS2 matches D13:D12.

Example 1: If D13 = LOW, D12 = HIGH and ADRS1 = LOW, ADRS2 = LOW, then the device is not

addressed since ADRS2 and D12 do not match.

Example 2: If D13/D12 = LOW and ADRS1/ADRS2 = LOW, then the device is addressed and all input data

is read and the attenuation settings updated.

D11, D10

Don’t care.

Figure 1. Microcontroller data input timing

Figure 2. Microcontroller data format

D15 D14 D13 D12 D11 D10 D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

MDT

MCK

MLEN

MDT

D15 D14 D13 D12 D11 D10 D9

D8

D7

D6

D5

D4

D3

D2

D1

D0