38
Agere Systems Inc.
Preliminary Data Sheet
September 2001
T8535B/T8536B Quad Programmable Codec
Timing Characteristics
(continued)
PCM Interface Timing
(continued)
Double-Clocking Mode
As with the single-clocking mode, FS signifies the start
of frame on the PCM bus for all four channels and
occurs every 125
μ
s at an 8 kHz rate. FS must be
synchronous with BCLK and must be high for a mini-
mum of one BCLK period. The PCM interface operates
using fixed data rate timing; data timing for both trans-
mit and receive are controlled by BCLK. In double-
clocking mode, however, BCLK runs at twice the PCM
data rate. BCLK can be any value from 512 kHz (data
rate of 256 kbits/s, 4 time slots) to 16.384 MHz (data
rate of 8192 kbits/s, 128 time slots) as defined by Table
19.
In Figure 26, detail A, the falling edge of the first BCLK
latches FS. The falling edge of the second BCLK
latches DR (receive bit offset of 1). DX starts on the ris-
ing edge of the first BCLK. The PCM bus transfers the
most significant bit of the data first.
The codec defaults to FS and DR being latched on the
first BCLK cycle. To latch DR on the second BCLK
cycle, program receive bit offset for 1 (RXBITOFF =
0x20). For every bit programmed (0 to 7), bit offset
shifts transmit or receive data by one BCLK cycle.
Therefore, in double-clock mode, the time-slot assign-
ment and bit offset registers need to be used in tandem
in order to achieve a full range of bit offset values. For
instance, in time-slot 0, bit offset will shift data up to
four bits. To shift data 5 to 8 bits, time slot 1 needs to
be selected.
Linear coding is not allowed in double-clocking mode.
TSX0 or TSX1 (not shown in Figure 26) is active (low)
when DX data is transmitting.
Note that the device reverts back to single-clock mode
if reset (address 128, bit 0). Internal states of the codec
can be reset without going out of double-clock mode
(address 128, bit 1).
Table 19. PCM Interface Timing: Double-Clocking Mode
(See Figure 26.)
Note: DX load = 150 pF.
Symbol
fBCLK
Parameter
Signal
BCLK
Min
—
—
—
—
—
—
—
—
—
Typ
512
1024
1536
2048
3072
4096
8192
16384
—
Max
—
—
—
—
—
—
—
—
Unit
kHz
kHz
kHz
kHz
kHz
kHz
kHz
kHz
—
Allowable BCLK Frequencies
—
Jitter of BCLK
BCLK
100 ns in
100 ms =
1 ppm
1953
8
tBCL x 0.6
15
—
—
tBCL
50
—
9
9
—
—
tBCL
tR, tF
tWL, tWH
tR, tF
tWFH
tWFL
tSF
tHF
tDDC
tDDF
tSD
tHD
Clock Period
Clock Rise/Fall
Pulse Width
Frame Rise/Fall
Frame Width High
Frame Width Low
Frame Setup
Frame Hold
Data Delay Clock
Data Delay Frame
Data Setup
Data Hold
BCLK
BCLK
BCLK
FS
FS
FS
FS
FS
DX
DX
DR
DR
61
—
—
—
—
—
—
—
—
—
—
—
—
—
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
tBCL x 0.4
—
tBCL
tBCL
7
4
—
—
7
4