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AD73311L Scheda tecnica(PDF) 28 Page - Analog Devices |
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AD73311L Scheda tecnica(HTML) 28 Page - Analog Devices |
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28 / 37 page  REV. A AD73311L –27– Interrupts The AD73311L transfers and receives information over the serial connection from the DSP’s SPORT. This occurs following reset—during the initialization phase—and in both Data-Mode and Mixed-Mode. Each transfer of data to or from the DSP can cause a SPORT interrupt to occur. However, even in FSLB configuration where serial transfers in and out of the DSP are synchronous, it is important to note that Tx and Rx interrupts do not occur at the same time due to the way that Tx and Rx inter- rupts are generated internally within the DSP’s SPORT. This is especially important in time-critical control loop applications where it may be necessary to use Rx interrupts only, as the relative positioning of the Tx interrupts relative to the Rx interrupts in a single sample interval are not suitable for quick update of new DAC positions. Initialization Following reset, the AD73311L is in its default condition, which ensures that the device is in Control Mode and must be programmed or initialized from the DSP to start conversions. As communications between AD73311L and the DSP are interrupt driven, it is usually not practical to embed the initialization codes into the body of the initialization routine. It is more practical to put the sequence of initialization codes in a data (or program) memory buffer and to access this buffer with a pointer that is updated on each interrupt. If a circular buffer is used, it allows the interrupt routine to check when the circular buffer pointer has wrapped around—at which point the initialization sequence is complete. In FSLB configurations, a single control word per codec per sample period is sent to the AD73311L whereas in nonFSLB, it is possible to initialize the device in a single sample period provided the SCLK rate is programmed to a high rate. It is also possible to use autobuffering, in which case an interrupt is generated when the entire initialization sequence has been sent to the AD73311L. Running the AD73311L with ADCs or DACs in Power-Down The programmability of the AD73311L allows the user flexibility in choosing which sections of the AD73311L need be powered up. This allows better matching of the power consumption to the application requirements as the AD73311L offers an ADC and a DAC in any combination. The AD73311L always interfaces to the DSP in a standard way regardless of whether the ADC or DAC sections are enabled or disabled. Therefore, the DSP will expect to receive an ADC samples per sample period and to transmit two DAC samples per sample period. If the ADC is disabled (in power-down), its sample value will be invalid. Like- wise, a sample sent to a DAC that is disabled will have no effect. There are two distinct phases of operation of the AD73311L: initialization of the device via the control registers, and operation of the converter sections of each codec. The initialization phase involves programming the control registers of the AD73311L to ensure the required operating characteristics such as sampling rate, serial clock rate, I/O gain, etc. There are several ways in which the DSP can be programmed to initialize the AD73311L. These range from hard-coding a sequence of DSP SPORT Tx register writes with constants used for the initialization words, to putting the initialization sequence in a circular data buffer and using an autobuffered transmit sequence. Hard-coding involves creating a sequence of writes to the DSP’s SPORT Tx buffer which are separated by loops or instructions that idle and wait for the next Tx interrupt to occur as shown in the code below. ax0 = b#1000000100000100; tx0 = ax0; idle; {wait for tx register to send current word} The circular buffer approach can be useful if a long initialization sequence is required. The list of initialization words is put into the buffer in the required order. .VAR/DM/RAM/CIRC init_cmds[8]; {Codec init sequence} .VAR/DM/RAM stat_flag; .INIT init_cmds: b # 1 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 , b # 1 0 0 0 0 0 1 0 1 1 1 1 1 0 0 1 , b # 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 , b # 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 , b # 1 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 , b # 1 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 , b # 1 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 , b # 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 , and the DSP program initializes pointers to the top of the buffer i3 = ^init_cmds; l3 = %init_cmds; and puts the first entry in the DSP’s transmit buffer so it is available at the first SDOFS pulse. ax0 = dm(i3,m1); tx0 = ax0; The DSP’s transmit interrupt is enabled. imask = b#0001000000; At each occurrence of an SDOFS pulse, the DSP’s transmit buffer contents are sent to the SDI pin of the AD73311L. This also causes a subsequent DSP Tx interrupt which transfers the initialization word, pointed to by the circular buffer pointer, to the Tx buffer. The buffer pointer is updated to point to the next unsent initialization word. When the circular buffer pointer wraps around, which happens after the last word has been accessed, it indicates that the initialization phase is complete. This can be done “manually” in the DSP using a simple address check or auto- buffered mode can be used to the complete transfer automatically. txcdat: ar = dm(stat_flag); ar = pass ar; if eq rti; ena sec_reg; ax0 = dm (i3, m1); tx0 = ax0; ax0 = i3; ay0 = ^init_cmds; ar = ax0 - ay0; if gt rti; ax0 = 0x00; dm (stat_flag) = ax0; rti; |
Codice articolo simile - AD73311L_17 |
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Descrizione simile - AD73311L_17 |
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