11/15
STA120
Professional Channel Status (C0 = 0)
When C0 is low, the received channel status block is encoded according to the professional / broadcast
format. The Ca through Ce pins are defined for some of the more important professional bits. As listed in
Table 5, Ca is the inverse of channel status bit1. Therefore, if the incoming channel status bit1. Therefore,
if the incoming channel status bit 1 is 1, Ca, defined as C1, will be 0. C1 indicates whether audio (C1 = 1)
or non-audio (C1 = 0) data is being received. Cb and Cc, defined as EM0 and EM1 respectively, indicate
emphasis and are encoded version of channel status bits 2, 3, and 4. The decoding is listed in Table 6.
Cd, defined as C9, is the inverse of channel status bit 9, which gives some indication of channel status bit
9, which gives some indication of channel mode. (Bit 9 is also defined as bit 1 of byte 1). When Ce, defined
as CRCE, is low, the STA120 calculated CRC value does not match the received CRC value. This signal
may be used to qualify Ca through Cd. If Ca through Ce are being displayed, Ce going low can indicate
not to update the display.
Table 6. Emphasis Encoding
Consumer Channel Status (C0 = 1)
When C0 is high, the received channel status block is encoded according to the consumer format. In this
case Ca through Ce are defined differently as shown in Table 5.
Ca is the inverse of channel status bit 1, C1, indicating audio (C1 = 1) or non-audio (C1 = 0). Cb is defined
as the inverse of channel status bit 2, C2, which indicates copy inhibit/copyright information Cc, defined
as C3
, is the emphasis bit of channel status, with C3 low indicating the data has had pre-emphasis added.
The audio standards, in consumer mode, describe bit 15, L, as the generation status which indicates
whether the audio data is an original work or a copy (1st generation or higher). The definition of the Lbit is
reversed for three category codes: two broadcast codes, and laser-optical (CD's). Therefore, to interpret
the L bit properly, the category code must be decoded. The STA120 does this decoding internally and pro-
vides the ORIG
signal that, when low, indicates that the audio data is original over all category codes.
SCMS
The consumer audio standards also mention a serial copy management system, SCMS, for dealing with
copy protection of copyrighted works. SCMS is designed to allow unlimited duplication of the original work,
but no duplication of any copies of the original. This system utilizes the channel status bit 2, Copy, and
channel status bit 15, L or generation status, along with the category codes. If the Copy bit is 0, copyright
protection is asserted over the material is an original or a duplication. (As mentioned in the previous para-
graph, the definition of the L bit can be reversed based on the category codes.) There are two category
codes that get special attention: general and A/D converters without C or L bit information. For these two
categories the SCMS standard requires that equipment interfacing to these categories set the C bit to 0
(copyright protection asserted) and the L bit to 1 (original). To support this feature, Ce, in the consumer
mode, is defined as IGCAT
(ignorant category) which is low for the "general" (0000000) and "A/D convert-
er without copyright information" (01100xx) categories.
EM1 EM0 C2 C3 C4 Emphasis
0 0 1 1 1 CCITT J.17 emphasis
0 1 1 1 0 50/15ms emphasis
1 0 1 0 0 No emphasis
1 1 0 0 0 Not indicated
