CS8420-CSZ datasheet(86/94 Pages) CIRRUS

86 / 94 page

DS245F4

CS8420

transmitter can read out data that had previously accumulated, allowing the FIFO to empty out. If the FIFO

becomes completely empty, zeros are transmitted until a complete message is written into the FIFO.

Mode 4 is not fail-safe; the FIFO can still get completely full if there isn't enough “zero-padding” between

incoming messages. It is up to the user to provide proper padding, as defined below:

Minimum padding

= (Fsi/Fso - 1)*[8N + (N-1)*IF +9] + 9

where N is the number of IUs in the message, IF is the number of filler bits between each IU, and Fso

≤ Fsi.

Example 1: Fsi/Fso = 2, N=4, IF=1: minimum proper padding is 53 bits.

Example 2: Fsi/Fso = 1, N=4, IF=7: min proper padding is 9 bits.

The CS8420 detects when an overwrite has occurred in the FIFO, and synchronously resets the entire

FIFO structure to prevent corrupted U data from being merged into the transmitted AES3 data stream.

The CS8420 can be configured to generate an interrupt when this occurs.

Mode 4 is recommended for properly formatted U data where mode 3 cannot provide acceptable perfor-

mance, either because of a too-extreme Fsi/Fso ratio, or because it's unacceptable to change the lengths

of filler segments. Mode 4 provides error-free performance over the complete range of Fsi/Fso ratios (pro-

vided that the input messages are properly zero-padded for Fsi > Fso).

CS8420-CSZ Datasheet(PDF) 86 Page - Cirrus Logic