User's Manual

22 68P80801H45-1 1/20/2002
Base Radio Controllers EBTS System Manual - Vol 2
900 MHz QUAD Channel Base Radio Controller
❐ electrical interface to the Ethernet transceiver
An isolation transformer provides high-voltage protection. The transformer also
isolates the Ethernet Serial Interface (ESI) and the transceiver. The pulse
transformer has the following characteristics:
❐ Minimum inductance of 75 µH
❐ 2000 V isolation between primary and secondary windings
❐ 1:1 Pulse Transformer
The Coaxial Transceiver Interface (CTI) is a coaxial cable line driver and receiver
for the Ethernet. CTI provides a 10Base2 connection via a coaxial connector on the
board. This device minimizes the number of external components necessary for
Ethernet operations.
A DC/DC converter provides a constant voltage of -9 Vdc for the CTI from a
3.3 Vdc source.
The CTI performs the following functions:
❐ Receives and transmits data to the Ethernet coaxial connection
❐ Reports any collision that it detects on the coaxial connection
❐ Disables the transmitter when packets are longer than the legal length
(Jabber Timer)
Digital Signal Processors
The BRC includes two Receive Digital Signal Processors (RXDSPs) and a Transmit
Digital Signal Processor (TXDSP). These DSPs and related circuitry process
compressed station transmit and receive audio or data. The related circuitry
includes the TDMA Infrastructure Support IC (TISIC) and the TISIC Interface
Circuitry. The DSPs only accept input and output signals in digitized form.
The RXDSP inputs are digitized receiver signals. The TXDSP outputs are digitized
voice audio and data (modulation signals). These signals pass from the DSP to the
Exciter portion of the EXBRC. DSPs communicate with the Microprocessor via an
eight-bit, host data bus on the host processor side. For all DSPs, interrupts drive
communication with the host.
The RXDSPs operate from an external 16.8 MHz clock, provided by the local
station reference. The RXDSP internal operating clock signal is 150MHz,
produced by an internal Phase-Locked Loop (PLL).
The RXDSPs accept digitized signals from the receivers through Enhanced
Synchronous Serial Interface (ESSI) ports. Each of two ESSI ports on a RXDSP
supports a single carrier (single receiver) digital data input. The DSP circuitry
includes two RXDSPs. These allow processing of up to four carriers (four
receivers).
The RXDSP accesses its DSP program and signal-processing algorithms in 128k
words of internal memory. The RXDSPs communicate with the host bus over an
8-bit interface.
Each RXDSP provides serial communications to its respective receiver module for
receiver control via a Serial Peripheral Interface (SPI). The SPI is a