CMX969 Просмотр технического описания (PDF) - MX-COM Inc

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CMX969

MOTIENT/ARDIS RD-LAP MDC4800 Modem

MX-COM Inc  

MOTIENTSM/ARDISSM RD-LAPTM MDC4800 Modem

13

CMX969 Advance Information

4.5.2.3 Control Register B4: ALTCRC - Alternative CRC

This bit should always be set to ‘0’ for standard RD-LAP and MDC systems. Setting it to ‘1’ in RD-LAP mode

selects an alternative CRC generation/checking algorithm.

4.5.2.4 Control Register B3: ALTFILT - Alternative Filtering

This bit should always be set to ‘0’ for standard RD-LAP and MDC systems. Setting it to ‘1’ in RD-LAP mode

selects slightly different transmit and receive lowpass filter characteristics more suitable for some non-

standard systems.

4.5.2.5 Control Register B2: MDC - MDC Mode

If this bit is ‘0’ the CMX969 operates in RD-LAP mode, setting this bit to ‘1’ selects MDC mode. Changing

between RD-LAP and MDC modes will cancel any current task.

4.5.2.6 Control Register B1: FSTOL - Frame Sync Detect Tolerance

In RD-LAP mode, this bit affects the number of errors tolerated by the Frame Sync detector. The allowable

errors are approximately 3 bits when FSTOL = 0, 7 bits when FSTOL = 1. In MDC mode, this bit has no effect

and the Frame Sync detector will accept up to 5 incorrect bits in a received Frame Sync pattern.

4.5.2.7 Control Register B0: HOLD - Freeze Rx Level and Timing Corrections

Setting this bit to 1 disables the receive level and symbol timing error correction circuits.

4.5.3 Mode Register

The contents of this 8-bit write only register control the basic operating modes of the modem:

Mode Register

765432 10

INVSYM

ZP

SSIEN SSYM

IRQEN

TX/RX

PSAVE

4.5.3.1 Mode Register B7: IRQEN - IRQ Output Enable

When this bit is set to '1', the IRQ chip output pin is pulled low (to VSS) whenever the IRQ bit of the Status

Register is a '1'.

4.5.3.2 Mode Register B6: INVSYM - Invert Symbols

This bit controls the polarity of the transmitted and received symbol voltages.

B6 Symbol

0

'+3 or +1'

'-3 or -1'

Signal at TXOUT

Above VBIAS

Below VBIAS

Signal at RXFB

Below VBIAS

Above VBIAS

1

'+3 or +1'

'-3 or -1'

Below VBIAS

Above VBIAS

Above VBIAS

Below VBIAS

4.5.3.3 Mode Register B5: TX/RX - Tx/Rx Mode

Setting this bit to '1' puts the modem into Transmit mode, clearing it to '0' puts the modem into Receive mode.

Note that changing between receive and transmit modes will cancel any current task.

¤2001 MX-COM, Inc.

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

Doc. # 20480211.002

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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