T7121-EL2 Ver la hoja de datos (PDF) - Agere -> LSI Corporation
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T7121-EL2 Datasheet PDF : 68 Pages
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Data Sheet
April 1997
T7121 HDLC Interface for ISDN (HIFI-64)
Functional Description (continued)
When HWYEN = 1 and DXAC = 1, pin 17 TSCA is low during unmasked bits of the selected time slot. Otherwise
TSCA is high.
The transmitter begins transmission when the transmitter enable ENT bit (R6—B3) is set to 1. Once the ENT bit is
enabled, user data is transmitted on the selected transmit data pin(s) (DXA, DXB, both, or neither). If the transmit-
ter is enabled and no transmit data pin has been selected, the HIFI-64 3-states both pins and the FIFO empties as
if the data were being transmitted. When the transmitter is disabled (ENT = 0), the transmitter continuously trans-
mits 1s on the selected transmit data pin(s) (DXA, DXB, or both). If neither DXA nor DXB is selected, both pins are
3-stated. The microprocessor can load the FIFO as normal while the transmitter is disabled. Disabling the transmit-
ter does not cause a transmitter reset. When the transmitter is disabled after having been enabled, the transmitter
should be reset via a TRES (R6—B5) = 1. Table 3 summarizes the transmit pin behavior based on the four register
bits that can affect it. This table assumes that P17CTL is set to 0 and that, in TDM highway modes, at least one
data bit is unmasked.
Table 3. Transmit Pin Behavior
HWYEN ENT DXAC DXBC*
(R0—B7) (R6—B3) (R7—B7) (R7—B6)
0
0
X
X
0
1
0
0
0
1
0
1
0
1
1
0
0
1
1
1
1
0
0
0
DXA
(Pin 19)
3-state
3-state
3-state
user data
user data
3-state
1
0
0
1
0
1
1
0
1
1
1
0
1
1
0
1
1
1
1
1
1
* P17CTL = 0 is assumed.
1
3-state
0
1s
1
1s
0
3-state
1
3-state
0
user data
1
user data
DXB
(Pin 17)
3-state
3-state
user data
3-state
user data
3-state
1s
3-state
1s
3-state
user data
3-state
user data
Comments
Reset condition.
Data can be lost.
—
—
—
Concentration highway interface
enabled.
Transmit 1s during user-programmed
time slot until transmitter is enabled.
Data can be lost.
—
—
—
The edge of CLKX (pin 18) used for data transmission is programmable by using CLKXI (R9—B4). Setting CLKXI
to 1 causes the T7121 to transmit data using the positive edge, while setting CLKXI to 0 enables transmission on
the negative edge (DEFAULT). Whenever the clock edge is changed, the transmitter should be reset via TRES
(R6—B5). When a gated clock is used to begin transmission on the first programmed clock edge, the opposite
clock edge must be provided first, after the reset. For example, if a gated clock with a negative edge transmission
is used, a positive edge of the clock should be provided first. This extra edge is only necessary on initial enabling of
the transmitter.
Lucent Technologies Inc.
11
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