Comtech EF Data SMS-758 - Manual (Page 62)

Theory of Operation SMS-758 Modem Protection Switch
4–2 MN/SMS758 Rev. 3
4.1.1 Theory of Operation
The M&C module uses an Intel 80C31 microcontroller operating at 5.5295 MHz.
The microsystem supports:
•
128K bytes of Read-Only Memory (ROM) for code.
•
64K bytes of Random-Access Memory (RAM) for data.
Of the 64K bytes, only 8K is used for RAM, and the remaining 56K is used for memory-
mapped I/O.
Memory-mapped I/O includes:
•
Real time clock/memory.
•
8-channel analog-to-digital converter.
•
External buffered bus structure for overall switch control and status gathering.
The 80C31 microcontroller supports a serial asynchronous communications channel
(RS-232C), with a maximum baud rate of 9600 bit/s using the 5.5295 MHz reference.
A rechargeable battery maintains the system real time clock and switch configuration
through power-down situations. Memory is maintained up to 30 days without power. A
full battery charge is attained after the switch is powered ON for 48 hours.
4.1.2 M&C Serial Interface
The M&C communicates with the address decoder/driver through an RS-232C interface.
To set the M&C for RS-232C operation:
1. Remove JP1, JP2, and JP3. Install JP4, JP5, and JPX.
2. Install JP7 at RS-232 location.
Note: The M&C should always be set up this way, even when using external RS-485
communications.