User Manual

CIRCUIT ANALYSIS
6.1 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.
6.2 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.
In this case, the outputs are always enabled, so the OE/ pins are tied low. Section 1 is
used for signals, which only go from the microprocessor to the Modems, so Pin 1 (1DIR)
is tied high. Section 2 is used for the bi-directional bus. Pin 24 (2DIR) is driven by logic
which sets the direction from microprocessor to Modems (high) most of the time. Only
during a read of one of the microprocessors is the direction reversed (low).
6.3 Microprocessor
The 80C323 microprocessor is a 3.3V version of the Dallas Speedy micro, an 80C32
derivative. It operates on a 14.7462 MHz. Clock, which is convenient for generating
standard baud rates. It interfaces with the Modems, Code RAM, Dual Port RAM, and
Data RAM via standard address and data busses.
The microprocessor has 2 asynchronous serial ports (TXD0/RXD0 and TXD1/RXD1)
which may be used in the SitePro system for diagnostics. Both ports are available on the
rear of the SitePro shelf.
Six bits of 80C323 microprocessor I/O are used in a SitePro configuration. WALCLK,
WAL1, WAL2, and HSACQCTL are outputs, while LSRX and MODFSL are inputs.
The microprocessor has only two level sensitive interrupts, INT0/ and INT1/. The first,
INT0/, is used for all Modem interrupts. The second, INT1/, is used for interrupts from
the Dual Port Ram.
Since it is still necessary to distinguish between the three Modem interrupts, RFINT/ and
PLINT/ are brought to I/O pins so the microprocessor can easily determine which
Modem is interrupting. i.e. If a Modem interrupt occurs, the microprocessor looks at the
two pins. If either or both are low, the corresponding interrupts are serviced. If neither is
low, the VDI interrupt is serviced.
The 80C323 (U1) uses standard Intel multiplexed address/data bussing. During the first
half of the bus cycle, U7 latches the lower 8 bits of address under the control of ALE.
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