MX919B 查看數據表（PDF） - MX-COM Inc

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MX919B

4-Level FSK Modem Data Pump

MX-COM Inc  

4-Level FSK Modem Data Pump

Page 15 of 47

MX919B PRELIMINARY INFORMATION

A SYMBOL FRAME

SYNC SYNC

B SYMBOL FRAME

SYNC SYNC

C SYMBOL FRAME

SYNC SYNC

'HEADER' BLOCKS

'INTERMEDIATE' BLOCKS

'INTERMEDIATE' BLOCKS

'LAST'

BLOCK

Figure 8: Alternative Frame Structures

The MX919B performs the entire block formatting and de-formatting required to convert data between µC

binary form and Over-Air as shown in Figure 7.

4.5 The Programmer’s View

To the programmer, the modem appears as 4 write only 8-bit registers, shadowed by 3 read only registers.

The individual registers are selected by the A0 and A1 chip inputs:

A1 A0

Write to Modem

0 0 Data Buffer

0 1 Command Register

1 0 Control Register

1 1 Mode Register

Read from Modem

Data Buffer

Status Register

Data Quality Register

Not used

Note: There is a minimum time allowance between accesses of the modem's registers, see Section 6.1.4.

4.5.1 Data Block Buffer

This is a 12-byte read/write buffer used to transfer data (as opposed to command, status, mode, data quality

or control information) between the modem and the host µC.

To the µC, the Data Block Buffer appears as a single 8-bit register. The modem ensures that sequential µC

reads or writes to the buffer are routed to the correct locations within the buffer.

The µC should only access this buffer when the Status Register BFREE (Buffer Free) bit is '1'.

The buffer should only be written to while in Tx mode and read from while in Rx mode. Note that in receive

mode, the modem will function correctly even if the received data is not read from the Data Buffer by the µC.

4.5.2 Command Register

Writing to this register tells the modem to perform a specific task as indicated by the TASK bits and modified

by the AQSC, AQLEV, CRC, and TXIMP bits.

Command Register

76543210

AQSC AQLEV CRC TXIMP Reserved

Set to '0'

TASK

When there is no action to perform, the modem will be in an 'idle' state. If the modem is in transmit mode, the

input to the Tx RRC filter will be connected to VBIAS. In receive mode, the modem will continue to measure

the received data quality and extract symbols from the received signal, supplying them to the de-interleave

buffer, otherwise these received symbols are ignored.

©2001 MX•COM, INC.

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

Doc. # 20480170.003

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

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