MAX78615+PPMSLASHC01T datasheet(39/46 Pages) MAXIM

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Failure to decode a host packet will cause the selected

target to send a fail code (0xB0–0xBF) acknowledgement

depending on mode of failure. Masters wishing to simplify

could accept any unimplemented fail code as a Negative

Acknowledge.

If no target is selected or the condition of a received

packet is uncertain, no reply is sent. Timeouts can also

occur when data is corrupt or no target is selected. The

master should implement the appropriate timeout control

logic after approximately 50 byte times at the current baud

rate. When a first reply byte is received, the master should

check to see if it is an SSI header or an Acknowledge.

If so, the timeout timer is reset, and each subsequent

receive byte will also reset the timer. If no byte is received

within the timeout interval, the master can expect the

slave timed out and re-send a new command.

SPI Interface

The Maxim device operates as an SPI slave. The host

is expected to instigate and control all transactions. The

signals used for SPI communication are defined as:

●

SSB : (also known as CSB) the device SPI chip/

slave select signal (active low)

●

SCK : the clocking signal that clocks MISO and

MOSI (data)

●

SDI : (also known as MOSI) the data shifted into the

measurement device

●

SDO : (also known as MISO) the data shifted out of

the measurement device

In Maxim embedded-measurement devices, these sig-

nals may have alternate functionality depending upon the

device mode and/or firmware.

SPI Mode

The device operates as a slave in mode 3 (CPOL = 1,

CPHA == 1) and as such the data is captured on the rising

edge and propagated on the falling edge of the serial data

clock (SCK). Figure 19 shows a single-byte transaction

on the SPI bus. Bytes are transmitted/received MSB first.

Table 45. SSI Responses

REPLY CODE

DEFINITION

0xAA

Acknowledge with data

0xAB

Acknowledge with data (half duplex)

0xAD

Acknowledge without data.

0xB0

Negative Acknowledge (NACK).

0xBC

Command not implemented.

0xBD

Checksum failed.

0xBF

Buffer overflow (or packet too long).

- timeout -

Any condition too difficult to handle with a

reply.

Figure 19. Signal Timing on the SPI Bus

SCK

MSB

SDI

SDO

SSB

MAX78615+PPM

Isolated Energy Measurement Processor

for Polyphase Monitoring Systems

www.maximintegrated.com

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