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Product(s)

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STA020

Transparent Mode

In certain applications it is desirable to receive digital audio data with the STA120 and retransmit it with

the STA020D. In this case, channel status, user and validity information must pass through unaltered. For

studio environments, AES recommends that signal timing synchronization be maintained throughout the

studio. Frame synchronization of digital audio signals input to and output from a piece of equipment must

be within ±5%.

The transparent mode of the STA020D is selected by setting TRNPT, pin 24, high. In this mode, the CBL

pin becomes an input, allowing direct connection of the outputs of the STA120 to the inputs of the

STA020D as shown in Figure 18. The transmitter and receiver are synchronized by the FSYNC signal.

CBL specifies the start of a new channel status block boundry, allowing the transmit block structure to be

slaved to the block structure of the receiver.

In the transparent mode, C, U and V are now transmitted with the current audio sample as shown in Figure

5 (TRNPT high) and the dedicated channel status pins are ignored.

When FSYNC is a word clock (Format 2), CBL is sampled when left C, U, V are sampled. When FSYNC

is Left/Right, CBL is sampled when left C, U, V are sampled. The channel status block boundry is reset

when CBL transitions from low to high (based on two successive samples of CBL). MCK for the STA020D

is normally expected to be 128 times the sample frequency, in the trasparent mode MCK must be 256 Fs.

Professional Mode

Setting PRO low places the STA020D in professional mode as shown in Figure 6. In professional mode,

channel status bit 0 is transmitted as a one and bits 1, 2, 3, 4, 6, 7 and 9 can be controlled via dedicated

pins. The pins are actually the inverse of the identified bit.

For example, tying the C1 pin low places a one in channel status bit 1. As shown in the application Note,

Overview of AES/EBU Digital Audio Interface Data Structures, C1 indicates audio/non-audio; C6 and C7

determine the sample frequency and C9 allows the encoded channel mode to be stereophonic. EM1 and

EM0 determine emphasis and encode C2, C3, C4 as shown in Table 2. The dedicated channel status pins

are read at the appropriate time and are logically OR’ed with data input on the channel status port, C. In

Transparent Mode, these dedicated channel status pins are ignored and channel status bits are input at

the C pin.

Consumer Mode

Setting PRO high places the STA020D in consumer mode which redefines the pins as shown in Figure 7.

In consumer mode, channel status bit 0 is transmitted as a zero and channel status bits 2, 3, 8, 9, 15, 24

and 25 are controlled via dedicated pins.

The pins are actually the inverse of the bit so if pin C2 is tied high, channel status bit 2 will be transmitted

as a zero. Also, FC0 and FC1 are encoded versions of channel status bits 24 and 25, which define the

sample frequency.

When FC0 and FC1 are both high, the part is placed in a CD submode which activates the CD subcode

port. This submode is described in detail in the next section. Table 3 describes the encoding of C24 and

C25 through the FC1 and FC0 pins. According to AES/EBU standards, C2 is copy prohibit/permit. C3

specifies pre-emphasis, C8 and C9 define the category code and C15 identifies the generation status of

the transmitted material (i.e. first generation, second generation).

Table 2. Emphasis Encoding

EM1

EM0

C2

C3

C4

00

1

1

1

01

1

1

0

10

1

0

0

11

0

0

0