Register Read/Write Operation

MSB

LSB

RegisterIndex(or Address)

RegisterData

IDX6

IDX5

IDX4

IDX3

IDX2

IDX1

IDX0

D7

D6

D5

D4

D3

D2

D1

D0

HighImpedance

WhenReadModeisInstructed

A6

MS

MC

MDI

MDO

A5

A4

A3

A2

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

D7

D6

D5

D4

D3

D2

D1

D0

PCM1795

All read/write operations for the serial control port use 16-bit data words. Figure 41 shows the control data word

format. The most significant bit (MSB) is the read/write (R/W) bit. For write operations, the R/W bit must be set to

'0'. For read operations, the R/W bit must be set to '1'. There are seven bits, labeled IDX[6:0], that hold the

register index (or address) for the read and write operations. The least significant eight bits, D[7:0], contain the

data to be written to, or the data that was read from, and the register specified by IDX[6:0].

Figure 42 shows the functional timing diagram for writing or reading the serial control port. MS is held at a logic 1

state until a register must be written to or read from. To start the register write or read cycle, MS is set to logic 0.

Sixteen clocks are then provided on MC, corresponding to the 16 bits of the control data word on MDI and

readback data on MDO. After the eighth clock cycle has completed, the data from the indexed-mode control

register appears on MDO during the read operation. After the 16th clock cycle has completed, the data are

latched into the indexed-mode control register during the write operation. To write or read subsequent data, MS

must be set to '1' once.

Figure 41. Control Data Word Format for MDI

NOTE: Bit 15 is used for selection of write or read. Setting R/W = 0 indicates a write, while R/W = 1 indicates a read. Bits 14–8 are used for

the register address. Bits 7–0 are used for register data.

Figure 42. Serial Control Format

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