ADBMS1818ASWZ-R7 datasheet(53/92 Pages) AD

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Data Sheet

ADBMS1818

THEORY OF OPERATION

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Rev. B | 53 of 92

transmit CSB changes and short pulses are used to transmit data,

as explained in Table 43.

Table 43. Port B (Master) isoSPI Port Function

Communication Event (Port A SPI)

Transmitted Pulse (Port B isoSPI)

CSB Rising

Long +1

CSB Falling

Long –1

SCK Rising Edge, SDI = 1

Short +1

SCK Rising Edge, SDI = 0

Short –1

Operation with Port A Configured for isoSPI

On the other side of the isolation barrier (that is, at the other end

of the cable), the 2nd ADBMS1818 has ISOMD = VREG so that its

Port A is configured for isoSPI. The slave isoSPI port (Port A or

Port B) receives each transmitted pulse and reconstructs the SPI

signals internally, as shown in Table 44. In addition, during a read

command this port can transmit return data pulses.

Table 44. Port A (Slave) isoSPI Port Function

Received Pulse (Port A

isoSPI)

Internal SPI Port Action Return Pulse

Long +1

Drive CSB high

None

Long –1

Drive CSB low

Short +1

1. Set SDI = 1

Short –1 pulse if reading a

0 bit

Table 44. Port A (Slave) isoSPI Port Function (Continued)

Received Pulse (Port A

isoSPI)

Internal SPI Port Action Return Pulse

2. Pulse SCK

Short –1

1. Set SDI = 0

(No return pulse if not in

read mode or if reading a

1 bit)

2. Pulse SCK

The slave isoSPI port never transmits long (CSB) pulses. Further-

more, a slave isoSPI port only transmits short –1 pulses, never a +1

pulse. The master port recognizes a null response as a Logic 1.

Reversible isoSPI

When the ADBMS1818 is operating with Port A configured for

isoSPI, communication can be initiated from either Port A or Port B.

In other words, ADBMS1818 can configure either Port A or Port B

as a slave or master, depending on the direction of communication.

The reversible isoSPI feature permits communication from both

directions in a stack of daisy-chained devices. See Figure 84 for an

example schematic. Figure 85 shows the operation of the reversible

isoSPI.

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