MX809J Ver la hoja de datos (PDF) - MX-COM Inc

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componentes Descripción

Fabricante

MX809J

1200bps MSK Modem

MX-COM Inc  

MSK Modem

12

6 Application

MX809

6.1 Checksum Generation and Checking

6.1.1 Generation

The checksum generator takes the 48 bits from the 6 bytes loaded into the TX Data Buffer and divides them

into modulo-2 by the generating polynomial:

x15 + x14 + x13 + x11 + x4 + x2 + x1

It then takes the 15-bit remainder from the polynomial divider, inverts the last bit and appends an EVEN parity

bit generated from the initial 48 bits and the 15 bit remainder (with the last bit inverted). This 16 bit word is

used as the “Checksum”.

6.1.2 Checking

The checksum checker does two things:

1. It takes the first 63 bits of a received message, inverts bit 63, and divides them modulo-2 by the

generating polynomial:

x15 + x14 + x13 + x11 + x4 + x2 + x1

2. The 15 bits remaining in the polynomial divider are checked to make sure that they are all zero.

3. It generates an even parity bit from the first 63 bits of a received message and compares this bit with the

received parity (bit 64).

If the 15 bits in the polynomial divider are all zero and the two parity bits are equal, then the RX

Checksum True (Status Register bit 1) is set.

6.2 Modem Performance

Figure 3: Bit Error Rate vs. Signal-to-Noise Ratio

1998 MX-COM, Inc.

www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054

Doc. # 20480036.004

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA

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