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CMX980AL7

Digital Radio Baseband Processor

MX-COM Inc  

Digital Radio Baseband Processor

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CMX980A Advance Information

4.7.4.1 Data Interlock Mechanisms

There are three possible transmission data interlock mechanisms. It is recommended that the user should

always use one of these methods.

Software polling

Serial Clock when ready

Interrupt data demand

Software polling requires the user to first check that the FIFO is not full before writing each TxData word. This

may be accomplished by inspecting the relevant FIFO status bits before writing one or more TxData words.

The Serial Clock when ready method is a hardware interlock mechanism (enabled by setting the

TxHandshakeEn bit of ConfigCtrl1 Register active). The mechanism allows the user to write TxData words

without doing any FIFO checks: the hardware handshake is implemented by stopping the serial port clock

when the FIFO is full. To prevent a serial port lockout-condition, the handshake is only enabled once the

transmission frame has been initiated and is automatically disabled at the end of a frame. This mechanism

should be used with care, because stopping the clock will freeze all other serial port transfers (the serial port

clock SClk is common to all three serial ports), including access to auxiliary data converters and receive data.

Interrupt data demand is used to request data when the FIFO has reached a defined level. An interrupt is

generated when the data in the FIFO reaches the pre-defined level of “nearly” empty (1 word remaining) or

when the FIFO is “nearly” full (1 location available). In each case, the user is responsible for managing the

response latency in detecting and servicing the interrupt and for writing new data into the FIFO so that symbol

‘run-out’ does not occur.

4.7.4.2 Direct write to 79-tap filter mode

The FIFO and DQPSK modulator may be bypassed thus allowing the user direct access to the Tx filter chain

input. The 12-bit data words must be supplied to input holding registers at MCLK/512 samples/sec for both I

and Q channels. To allow a single serial-operation write, the TxDirectWrite79tapI and TxDirectWrite79tapQ

Registers are in the page 1 address map. By utilising the four least significant address bits to map to the most

significant bits of the data, a 12-bit data word can be transferred in a single serial-write frame.

4.7.4.3 Power Ramping and Frame Interlock

The RampUp bit in the TxData word is used to control both the power ramping function and the frame

activation. To start a transmission frame, a transmission word is written with the RampUp bit active. All

subsequent TxData words prior to frame termination must also have this bit active. The frame is terminated by

writing transmit data words with the RampUp bit inactive. Subsequent TxData words must also have this bit

inactive, until initiation of a new frame is required. While the power ramping is active, (up or down) the user

must supply transmission symbols or valid constellation points. Once the ramp down operation has

completed, all subsequent TxData writes with the RampUp bit inactive will be ignored.

4.7.5 Command Control Serial Word

A command word either directly accesses an internal register for a read or write operation, or addresses a

memory access point to indirectly access a block of internal memory. For test purposes all registers that can

be written may also be read. Not all registers may be written, as some are just status registers. Each register

or memory access point is assigned a unique address: the whole (8-bit) address range is reserved for the

CMX980A.

A page address technique is used to extend the available address space beyond the 128 locations allowed by

7-bit address fields. This gives four pages of 128 locations, of which the first two (page 0 and page 1) are

used. The device configuration and control registers ConfigCtrl1 and ConfigCtrl2 are accessible across all

pages, ConfigCtrl2 bits 6 and 7 forming the 2-bit page address.

2000 MX-COM, Inc.

www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054

Doc. 20480201.001

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

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