
Philips Semiconductors
PNX15xx Series
Volume 1 of 1
Chapter 17: SPDIF Output
PNX15XX_SER_3
Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Product data sheet
Rev. 3 — 17 March 2006
17-5
Programmers should refer to the IEC-60958
Digital Audio Interface, “Part 1:General;
Part 2: Professional Applications; Part 3: Consumer Applications” for a precise
description of the required values in each eld for different types of consumer
equipment.
The SPDO block hardware only generates B, W and M preambles as well as the P
(Parity) bit. All other bits in the sub-frame are completely determined by software and
copied “as is” from memory to output, subject only to bit-cell coding.
Software must construct valid IEC-60958 blocks by using the right sequence of 32-bit
IEC-60958 Bit Cell and Preamble
Each data bit in IEC-60958 is transmitted using bi-phase mark encoding. In bi-phase
mark encoding, each data bit is transmitted as a cell consisting of two consecutive
binary states. The rst state of a cell is always inverted from the second state of the
previous cell. The second state of a cell is identical to the rst state if the data bit
value is a “0”, and inverted if the data bit value is a “1”.
Preambles are coded as bi-phase mark violations, where the rst state of a cell is not
the inverse of the last state of the previous cell.
The duration of each state in a cell is called a UI (Unit Interval), so that each cell is 2
UIs long. In SPDO, the length of a UI is 1 SPDO clock cycle as determined by the
Figure 2 illustrates the transmission format of 8 bit data value “10011000”, as well as
the transmission format of the three preambles. Note that each preamble always
starts with a rising edge. This is made possible by the presence of the parity bit,
which always guarantees an even number of ‘1’ bits in each subframe.
Figure 2:
Bi-Phase Mark Data Transmission
“1”
“0”
“1”
“0”
UI
cell
bi-phase mark violation
NRZ
Bi-Phase Mark
B Preamble
M Preamble
W Preamble