FX829D2 CMLMICRO [CML Microcircuits], FX829D2 Datasheet - Page 18

• Manufacturer Part Number: FX829D2
• Description: Baseband Signal Processor
• Manufacturer: CMLMICRO [CML Microcircuits]

Baseband Signal Processor
SYNCF
(Bit 0)
RXDATA Register (Hex address $42)
This register contains the last byte of data received. It is updated every 8 bits at the same time as the
RXSUMF bit in the STATUS register is updated.
The RXDATA register is double buffered, thus giving the user up to 8 bit periods to read the data before it is
overwritten by the next byte.
1.5.2
1997 Consumer Microcircuits Limited
FFSK Checksum Generation and Checking
Generation
The checksum generator takes the m x 8 bits from the m bytes of information, sequentially loaded into
the TXDATA register and divides them modulo-2, by the generating polynomial:
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 m x 8 bits and the 15-bit remainder (with the last bit
inverted).
This 16-bit word is used as the "CHECKSUM". See Figure 5.
(m = the number of bytes in the information to be sent)
This bit is only defined when SYNC PRIME is enabled.
When the data sequence specified by SYNC has been successfully matched to the
Rx incoming data, this bit will be set to "1".
This bit is reset to "0" immediately after reading the STATUS register. When this
bit is set to "1", an interrupt will be generated, the checksum generator and byte
counter will be reset and SYNC PRIME, SYNT PRIME and RX SYNC WORD
PRIME will be reset.
X
Figure 5 Checksum Generation
15
+ X
14
+ X
13
18
+ X
11
+ X
4
+ X
2
+ 1
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