Comtech EF Data SNM-1002 - Manual (Page 99)

SNM-1002 LinkSync
 Modem
Revision 2
Theory of Operation MN/SNM1002.OM
4–5
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 equal to or greater than 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 data
rate of 19200 bit/s. The UART is a built-in peripheral of the microcontroller. The
communications type is EIA-232.
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.
All functions are memory-mapped to the micro-controller.
4.3 Modulator
The modulator provides PSK modulated carriers within the 50 to 180 MHz range. The
types of modulation that encode the transmitted baseband data from the interface PCB
are:
• BPSK
• QPSK
Refer to Section 4.2.3 for a description of each modulation type.
A block diagram of the modulator is shown in Figure 4-2.