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參數(shù)資料
| 型號： | T8538B |
| 元件分類： | Codec |
| 英文描述： | T8538B Quad Programmable Codec |
| 中文描述： | T8538B四可編程編解碼器 |
| 文件頁數(shù)： | 21/44頁 |
| 文件大?。?/td> | 847K |
| 代理商： | T8538B |
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Agere Systems Inc.
21
Preliminary Data Sheet
August 2001
T8538B Quad Programmable Codec
Functional Description
(continued)
SLIC Control Capabilities
Memory locations 158, 159, and 160 are used to con-
trol five or six bidirectional latches that allow the serial
interface to control other devices, such as ringing/test
switches, telecom electromechanical relays, and SLIC
devices. When the TTL latches are configured as out-
puts, external devices should be set up to sink current
from the latch. Location 158 sets the operational mode
of these latches as either inputs or outputs. Location
159 specifies what is to be written on the latch leads
driven by the device. Updates occur within one frame
(125
μ
s). Location 160 reports the actual state of these
leads. Latches are strobed every 125
μ
s (coincident
with frame strobe). It should be noted that a channel
control reset forces all of these external leads, except
those corresponding to bits 2 and 3, to the high-imped-
ance state, so any inputs connected to bits 0, 1, 4, and
5 should have appropriate pull-up or pull-down resis-
tors (off-chip, if required) to force the external device
into a known state at power-up or in the event of a
reset. Bits 2 and 3 will reset to outputs with a value of
zero.
The fast scan mode allows for a minimal data transfer
on the serial bus to monitor bits 0 and 1 of the SLIC
data memory location (159). If these 2 bits are wired as
inputs to the off-hook and/or ring ground detection cir-
cuits, a convenient method of rapidly scanning for
these two functions is obtained. Bits 2 and 3 default to
outputs; thus, they are convenient to provide control of
the SLIC state. In any event, all six leads are program-
mable for maximum flexibility.
Suggested Initialization Procedures
It is suggested that upon powerup, a hardware reset be
used to set the device into a known state. The serial
interface should then be used to load the memory
addresses that differ from the default values (the write
all channels command is convenient for this function).
If other devices are controlled by the SLIC data mem-
ory location, then it also should be loaded with a known
configuration. After the completion of this sequence,
the device is ready to be activated. Depending on the
application, the next step may either be normal opera-
tion or a set of test sequences. After the initialization of
the memory, the device and associated line card
devices can be controlled by using memory locations
130, 131, 145, 155, 156, 157, 158, 159, and 129; that
is, by supplying the PCM bus time-slot addresses,
switching the SLIC into the proper mode, and activating
the codec. Within memory location 129, the codec
would normally be placed into active mode with both
directions of the PCM bus enabled at the start of a call.
At the completion of a call, the codec should be placed
into standby mode and the PCM bus disabled. Great
caution should be used when changing the memory
while the codec is in active mode since termination
impedances, balance impedances, and gains may
change. These changes are likely to yield undesirable
system effects. It is safe to refresh coefficients that are
known to be unchanging in the application. It is always
possible to read the memory to verify its contents with-
out deleterious effects on codec operation. Normal
operation would load the memory and perform all gain
adjustments while the codec is in standby mode. Under
no circumstances should memory above address 162
be written, since this section of memory is used for
state data and intermediate results. Also, all reserved
addresses should not be written. Changing this infor-
mation may have deleterious effects on system opera-
tion.
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