AD1870 datasheet(12/20 Pages) AD

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AD1870

REV. A

–12–

Serial Port Data Timing Sequences

The RDEDGE input (Pin 6) selects the bit clock (BCLK) polarity.

RDEDGE HI causes data to be transmitted on the BCLK falling

edge and valid on the BCLK rising edge; RDEDGE LO causes

data to be transmitted on the BCLK rising edge and valid on

the BCLK falling edge. This is shown in the serial data output

timing diagrams. The term “sampling” is used generically to

denote the BCLK edge (rising or falling) on which the serial data is

valid. The term “transmitting” is used to denote the other BCLK

edge. The S/

M input (Pin 7) selects Slave Mode (S/M HI) or

Master Mode (S/

M LO). Note that in Slave Mode, BCLK may be

continuous or gated, i.e., a stream of pulses during the data phase

followed by periods of inactivity between channels.

In the Master Modes, the bit clock (BCLK), the left/right clock

RCK), and the word clock (WCLK) are always outputs, gen-

erated internally in the AD1870 from the master clock (CLKIN)

input. In Master Mode, a L

RCK cycle defines a 64-bit “frame.”

RCK is HI for a 32-bit “field” and LRCK is LO for a 32-

bit “field.”

In the Slave Modes, the bit clock (BCLK) and the left/right clock

RCK) are user-supplied inputs. The word clock (WCLK) is an

internally generated output, except when S/

M is HI, RLJUST is

HI, and

MSBDLY is LO when it is a user-supplied input that

controls the data position. Note that the AD1870 does not sup-

port asynchronous operation in Slave Mode; the clocks

(CLKIN, L

RCK, BCLK, and WCLK) must be externally

derived from a common source. In general, CLKIN should be

divided down externally to create L

RCK, BCLK, and WCLK.

In the Slave Modes, the relationship between L

RCK and BCLK

is not fixed to the extent that there can be an arbitrary number

of BCLK cycles between the end of the data transmission and

the next L

RCK transition. The Slave Mode timing diagrams are

therefore simplified as they show precise 32-bit fields and

64-bit frames.

In two Slave Modes, it is possible to pack two 16-bit samples in

a single 32-bit frame, as shown in Figures 15 and 16. BCLK,

RCK, DATA, and TAG operate at one-half the frequency

(twice the period) as in the 64-bit frame modes. This 32-Bit

Frame Mode is enabled by pulsing the L

RCK HI for a mini-

mum of one BCLK period to a maximum of 16 BCLK periods.

The L

RCK HI for one BCLK period case is shown in Figures 15

and 16. With a one or two BCLK period HI pulse on L

RCK,

note that both the left and right TAG Bits are output immedi-

ately, back to back. With a three-to-sixteen BCLK period HI pulse

on L

RCK, the left TAG Bits are followed by one to fourteen

“dead” cycles, i.e., zeros, followed by the right TAG Bits. Also

note that WCLK stays HI continuously when the AD1870 is

in the 32-Bit Frame Mode. Figure 15 illustrates the left-justified

case, while Figure 16 illustrates the I

2S-justified case.

In all modes, the left and right channel data is updated with the

next sample within the last 1/8 of the current conversion cycle, i.e.,

within the last four BCLK cycles in 32-Bit Frame Mode, and

within the last eight BCLK cycles in 64-Bit Frame Mode. The

user must constrain the output timing such that the MSB of the

right channel is read before the final 1/8 of the current con-

version period.

Two modes deserve special discussion. The first special mode,

Slave Mode, Data Position Controlled by WCLK Input

(S/

M = HI, RLJUST = HI, MSBDLY = LO), shown in

Figure 8, is the only mode in which WCLK is an input. The

16-bit output data-words can be placed at user-defined loca-

tions within 32-bit fields. The MSB will appear in the BCLK

period after WCLK is detected HI by the BCLK sampling edge.

If WCLK is HI during the first BCLK of the 32-bit field, i.e, if

WCLK is tied HI, then the MSB of the output word will be

valid on the sampling edge of the second BCLK. The effect is to

delay the MSB for one bit clock cycle into the field, making the

output data compatible at the data format level with the I

2S data

format. Note that the relative placement of the WCLK input

can vary from 32-bit field to 32-bit field, even within the

same 64-bit frame. For example, within a single 64-bit frame,

the left word could be right-justified (by pulsing WCLK HI on

the 16th BCLK) and the right word could be in an I

2S compat-

ible data format (by having WCLK HI at the beginning of the sec-

ond field).

In the second special mode, Master Mode, Right-Justified

with MSB Delay, WCLK Pulsed in 17th BCLK Cycle (S/

= LO, R

LJUST = HI, MSBDLY = LO), shown in Figure 12,

WCLK is an output and is pulsed for one cycle by the AD1870.

The MSB is valid on the 18th BCLK sampling edge, and the

LSB extends into the first BCLK period of the next 32-bit field.

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