MT312 查看數據表（PDF） - Zarlink Semiconductor Inc

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MT312

Satellite Channel Decoder

Zarlink Semiconductor Inc 

Functional Overview MT312

AGC control

RF I/P

I

Direct

Conversion

ZIF Tuner

Q

SL1935

Tank

Low pass

Filter

I I/P

Q I/P

Channel

Decoder

MT312

Transport

stream O/P

2-wire bus

control

2-wire bus control

Figure 13 - Alternative System Block Diagram - SNIM6

1.7 DiSEqC™ Transmit and Receive Messages

The MT312 has the capability to send and receive

DiSEqC™ messages. Eight registers are provided to

store a message for transmission and a further eight

registers are provided to store a received message.

The received bytes have a parity bit and a parity

error bit in addition to the eight data bits. These

additional bits are read out in following the data bits,

so two byte reads are required for each data byte.

1.7.1 DiSEqC™ Transmitting Messages

The sequence of events to send a message are as

follows:

1. Load the required message bytes into the

DiSEqC™ Instruction register 36, see page 34.

Sequential writes to the same register is achieved

by setting the Inhibit Auto Incrementing (IAI) bit 7

in RADD, the register address byte.

2. Load the number of bytes (less one) in the

DiSEqC™ instruction in the register

DISEQC MODE[5:3], see page 32.

3. Set DISEQC MODE[2:0] = 4 to command the

MT312 to encode the data and transmit the

message.

4. Reset DISEQC MODE[2:0] to either 0 or 1

depending on previous setting of 22kHz off or on.

transmitted. If a return message is expected, the

DISEQC MODE[2:0] must be set to zero in order to

leave the LNB control signal free for another

DiSEqC™ transmitter to respond.

The sequence of events to receive a message are as

follows:

1. Enable DiSEqC2 GPP2 pin 46 as an input by

setting GPP CTRL register 20 B5 to zero.

2. Enable interrupts if the IRQ pin is being used to

interrupt the host processor in DISEQC2 CTRL1

register 121.

3. Monitor DISEQC2 INT register.

4. If B3 = 1 and B1 = 0, there has been no message

received.

5. If a message has been received, B0 will be set, If

B1 is also set the message is complete.

DISEQC2 INT register B7-4 indicate how many

bytes have been received.

6. Read the received message from

DISEQC2 FIFO register 120 by setting the Inhibit

Auto Incrementing (IAI) bit 7 in RADD, the register

address byte and sequentially reading

DISEQC2 FIFO for the indicated number of

bytes. Each data byte read requires two 2-wire

bus reads. The second or the pair of bytes

contains the parity bit and a parity bit error

indicator.

The data loaded into DISEQC INSTR register is

retained, so that if the same message is to be

repeated, the data loading stage 1 above can be

omitted.

1.7.2 DiSEqC™ Receiving Messages

The MT312 will automatically listen for DiSEqC™

messages 5ms after a message has been

The user may choose to wait for the end of message

indication, before reading the message, if it is known

that the message is not greater than eight bytes.

However, if the length of message is not known, the

message should be read out of the FIFO by the host

as it is being received. Care must be taken to avoid a

FIFO buffer overflow. DISEQC2 INT register B7-4 will

indicate how many bytes remain in the FIFO.

17

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