User`s manual

Am186™CC Microcontroller Router Reference Design User’s Manual
2-20
ISDN U Interface
NOTE: See sheet 6 in the schematics for the ISDN U interface circuitry.
The Lucent T7237A U transceiver provides the two-wire 2B+D U interface for
terminal adapter functionality. The T7237A processes the ISDN BRI bit stream
that consists of two 64-Kbit/s B channels and a single 16-Kbit/s D channel.
The T7237A U transceiver uses the Am186CC microcontroller SSI interface to
configure itself; the T7237A’s time-division multiplexed (TDM) bus is used to
transfer data between itself and either the microcontroller’s integrated HDLC in
PCM mode, or the POTS interface.
The microcontroller’s SSI interface to the T7237A U transceiver’s serial interface
is controlled by U48D (location E-5) and PIO38 (see sheet 6 of the schematics).
U48D is required to select the T7237A U transceiver serial interface because the
T7237A does not have an SSI chip enable, and the Am186CC microcontroller
router reference design’s POTS interface DSLAC device also has an SSI interface.
U48D uses the Am186CC microcontroller’s PIO38 signal asserted Low to pass the
SSI clock to the T7237A U transceiver during T7237A configuration.
The T7237A U transceiver’s TDM bus is the PCM clock master and the upstream
device to the Am186CC microcontroller and the DSLAC device in the POTS
interface. In this configuration, the TDM bus drives the PCM data clock and frame
sync, and transmits data directly to and from the Am186CC microcontroller and
the DSLAC device in the POTS interface.
CR8 (location H-5) is used for T7237A U transceiver device status. Table 2-9
shows the U interface LED status.
Table 2-9. U Interface LED Status
CR8 State CR8 Function
Off Interface not active
1 Hz flashing U interface activation in progress
8 Hz flashing U interface active
On U and S/T interface fully active
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