Comtech EF Data SDM-300A - Manual (Page 43)

SDM-300A Satellite Modem Revision 6
Functional Description MN/SDM300A.IOM
2–3
The heart of the M&C card is the Dallas 80C310 microcontroller operating at 11 MHz. This
microcontroller contains 256 kbytes of internal RAM. The ROM at U8 is 29F040 (512 kbytes).
• ROM access times must be ≥ 150 ns. The RAM can be 8 or 32 kbytes in size.
• This RAM chip is internally battery-backed and contains a real time clock used by the
M&C.
The non-volatile RAM on the M&C module allows the module to retain configuration
information without prime power for 1 year (approximately). If the modem is powered down,
the following sequence is carried out by the M&C microcontroller.
1. When power is applied to the M&C, the microcontroller checks the non-volatile
memory to see if valid data has been retained. If valid data has been retained, the
modem is reconfigured to the parameters maintained by the RAM.
2. If the non-volatile memory fails the valid data test, a default configuration from ROM is
loaded into the system.
The UART supports serial ASYNC communications channels (remote port) with a maximum
data rate of 19200 bps. The UART is a built-in peripheral of the microcontroller. The
communications type can be RS-232, RS-485 (2-wire), RS-485 (4-wire), and software
selectable.
The DAC supplies a voltage that controls the contrast of the display. The ADC monitors all the
voltages from the power supply. The DAC and ADC are mapped to the microcontroller with an
Integrated Circuit (IC) bus.
The user interface includes the following parts:
• Front panel
• Status LEDs
• Keyboard
• Sounder (beeper)
All functions are memory-mapped to the microcontroller.