MAX86140 datasheet(54/89 Pages) MAXIM

54 / 89 page

Read mode operations will access the requested data

on the 16th SCLK rising edge, and present the MSB of

the requested data on the following SCLK falling edge,

allowing the µC to latch the data MSB on the 17th SCLK

rising edge. Configuration and status registers are avail-

able through normal mode readback sequences. FIFO

reads must be performed with a burst mode FIFO read

(see SPI FIFO Burst Mode Read Transaction). If more

than 24 SCLK rising edges are provided in a normal

read sequence, the excess edges will be ignored and the

device will read back zeros.

SPI FIFO Burst Mode Read Transaction

The MAX86140/MAX86141 provides a FIFO burst read

mode to increase data transfer efficiency. The first 16

SCLK cycles operate exactly as described for the normal

read mode, the first byte being the register address, the

second being a read command. The subsequent SCLKs

consist of FIFO data, 24 SCLKs per word. All words in

the FIFO should be read with a single FIFO burst read

command.

Each FIFO sample consists of 3 bytes per sample and thus

requires 24 SCLKs per sample to readout. The first byte

(SCLK 16 to 23) consists of a tag indicating the data type

of the subsequent bits. Following the tag is the MSBs of the

subsequent data (MSB, MSB-1, and MSB-2). The next byte

(SCLK 24 to 31) consists of data bits MSB-3 to MSB-19. The

final byte of each sample (SCLK 32 to 40) consists of the

data LSB bits. The number of words in the FIFO depends

on the FIFO configuration. See FIFO Configuration for

more details the FIFO configuration and readout.

Figure 38. SPI Read Transaction

Figure 39. SPI FIFO Burst Mode Read Transaction

Interrupt/Read Pointer Updated (If Applicable)

Ignored

Edges

CSB

SDI

SCLK

SDO

DON’T CARE

DO7 DO6 DO5 DO4 DO3 DO2 DO1 DO0

N+

DON’T CARE

CSB

SDI

SCLK

SDO

T4A

SCLK

SDO

CSB

T3A T2A T1A T0A O18A O17A O16A O15A O14A O13A O12A O11A O10A O9A O8A O7A O6A O5A O4A O3A O2A O1A O0A

N+

T4C

SCLK

SDO

T3C T2C T1C T0C O18C O17C O16C O15C O14C O13C O12C O11C O10C O9C O8C O7C O6C O5C O4C O3C O2C O1C O0C

T4B

SCLK

SDO

T3B T2B T1B T0B O18B O17B O16B O15B O14B O13B O12B O11B O10B O9B O8B O7B O6B O5B O4B O3B O2B O1B O0B

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