User Manual Part 1

CIRCUIT ANALYSIS
MM101271V1 R2A 41
7.4 SitePro MODEM BOARD
The SitePro Modem Board contains three synchronous serial ports (modems) and a local
microprocessor. This board plugs into the Controller Board using two connectors,
QUICC (J9) and I/O (J2). Refer to Figure 9 - Site Pro Modem Board Block Diagram.
The microprocessor interface is a simple 8-bit bus port with two separate chip selects.
One chip select controls access to an 8k x 8 dual port RAM. The other chip select
controls access to the Modem Board microprocessor local code memory. The Controller
Board microprocessor loads the Modem Board local code memory with code before
releasing the Modem Board reset. The Modem Board microprocessor runs from a 14.7
MHz clock generated by dividing down the 29.5 MHz Controller Board microprocessor
output clock inside the EPLD.
Circuits for the SitePro Modem Board, are shown on Schematic Diagram WD-
CB101074V1, Sheet 1. The Outline Diagram is shown on AD-CB101074V1.
Modem Board CB101074V1 mounts on the Controller Board and exists primarily to
support Modem chips, U9, U10, and U11. These modems process 9600 baud serial
synchronous receive and transmit data from the RF path (U9), the Phone Line (PL) path
(U10) and the Voted Digital Interconnect (VDI) path (U11).
Microprocessor U1, a Dallas 80C323, controls the three modem chips, generates transmit
data, and processes receive data for use by the system.
The microprocessor communicates with the QUICC processor on the Controller Board
via Dual Port RAM U3.
There is no non-volatile memory on the Modem Board. Code is loaded into Code RAM
(U2) via an interface from the QUICC processor.
The microprocessor circuitry on the Modem Board operates from a 3.3V supply. The
Modem chips, however, require 5V. Thus a 3.3V to 5V conversion (U6) is needed for all
signals to the Modem chips.
7.4.1 Modems
Each Modem chip interfaces to the 80C323 microprocessor via an 8-bit bi-directional
address/data bus, and Chip Select (CS/), Read (RD/), Write (WR/), ALE, and Interrupt
(INT/) signals.
During transmit the microprocessor writes data to the Modem as requested by the Modem
interrupt. The Modem converts the data to a 9600-baud synchronous serial data stream.
During receive the Modem chip receives the 9600-baud synchronous serial data stream
and interrupts the 80C323 microprocessor whenever it has a complete byte to transfer.
The modem must also acquire bit sync and word sync from the data stream.
7.4.2 3.3V/5V Interface
Because the Modems require a 5V supply, and the microprocessor is on a 3.3V supply, it
is necessary to convert the voltage of signals passing between them. This is done by U6,
an IDT74FCT164245 3.3V/5V converter. Both output enable and direction can be
controlled for the two 8-bit sections of this IC.