Rainbow Electronics DS26503 - Manual (Page 79)

DS26503 T1/E1/J1 BITS Element
79 of 123
13.2.2 Receive G.703 Section 10 Synchronization Signal
The DS26503 can receive a 2.048MHz square-wave synchronization clock as specified in Section 10 of
ITU G.703. To use the DS26503 in this mode, set the mode configuration bits in the Mode Configuration
Register (MCREG).
13.2.3 Monitor Mode
Monitor applications in both E1 and T1 require various flat gain settings for the receive-side circuitry.
The DS26503 can be programmed to support these applications via the monitor mode control bits MM1
and MM0 in the LIC3 register.
Figure 13-2. Typical Monitor Application
13.3 LIU Transmitter
The DS26503 uses a phase-lock loop along with a precision digital-to-analog converter (DAC) to create
the waveforms that are transmitted onto the E1 or T1 line. The waveforms created by the DS26503 meet
the latest ETSI, ITU, ANSI, and AT&T specifications. The waveform that is to be generated is set by the
transmit mode bits (TMODE[3:0]) in the MCREG register, as well as the L2/L1/L0 bits in register LIC1
if applicable.
ITU specification G.703 requires an accuracy of ±50ppm for both T1 and E1. TR62411 and ANSI specs
require an accuracy of ±32ppm for T1 interfaces. The transmit clock can be sourced from the recovered
clock (RCLK), the pre-scaled MCLK, the TCLK pin or the TX PLL. See the TX PLL clock mux diagram
in
Figure 3-3 . Due to the nature of the design of the transmitter in the DS26503, very little jitter (less than
0.005 UI
P-P
broadband from 10Hz to 100kHz) is added to the jitter present on the selected transmit clock
source. Also, the waveforms created are independent of the duty cycle of TCLK. The transmitter in the
DS26503 couples to the transmit twisted pair (or coaxial cable in some applications) via a 1:2 step-up
transformer. For the device to create the proper waveforms, the transformer used must meet the
specifications listed in
Table 13-1 . The DS26503 has the option of using software-selectable transmit
termination.
PRIMARY
T1/E1 TERMINATING
DEVICE
MONITOR
PORT JACK
T1/E1 LINE
X
F
M
R
DS26503 Rt
Rm Rm
SECONDARY T1/E1
TERMINATING
DEVICE