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AD73322L Fiches technique(PDF) 39 Page - Analog Devices |
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AD73322L Fiches technique(HTML) 39 Page - Analog Devices |
39 / 49 page AD73322L Rev. A | Page 38 of 48 INITIALIZATION Following reset, the AD73322L 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. Because communications between AD73322L and the DSP are interrupt driven, it is usually not practical to embed the initial- ization 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 AD73322L. 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 AD73322L. RUNNING THE AD73322L WITH ADCS OR DACS IN POWER-DOWN The programmability of the AD73322L allows the user flexi- bility in choosing what sections of the AD73322L need to be powered up. This allows better matching of the power con- sumption and application requirements, because the AD73322L offers two ADCs and two DACs in any combination. The AD73322L always interfaces to the DSP in a standard way, regardless of what ADC or DAC sections are enabled or disabled. Therefore, the DSP expects to receive two ADC samples per sample period and to transmit two DAC samples per sample period. If a particular ADC is disabled (in power- down) then its sample value is invalid. Likewise, a sample sent to a DAC which is disabled has no effect. There are two distinct phases of operation of the AD73322L: initialization of the device via each codec section’s control registers, and operation of the converter sections of each codec. The initialization phase involves programming the control registers of the AD73322L to ensure the required operating characteristics such as sampling rate, serial clock rate, and I/O gain. There are several ways in which the DSP can be programmed to initialize the AD73322L. 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 that follows. ax0 = b#1000100100000100; tx0 = ax0; idle; {wait for tx register to send current word} The circular buffer approach can be useful if a long initiali- zation sequence is required. The list of initialization words is put into the buffer in the required order: .VAR/DM/RAM/CIRC init_cmds[16]; {Codec init sequence} .VAR/DM/RAM stat_flag; .INIT init_cmds: b # 1 0 0 0 1 0 0 1 0 0 0 0 0 1 0 0 , b # 1 0 0 0 0 0 0 1 0 0 0 0 0 1 0 0 , b # 1 0 0 0 1 0 1 0 1 1 1 1 1 0 0 1 , b # 1 0 0 0 0 0 1 0 1 1 1 1 1 0 0 1 , b # 1 0 0 0 1 0 1 1 0 0 0 0 0 0 0 0 , b # 1 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 , b # 1 0 0 0 1 1 0 0 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 1 1 0 1 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 1 1 1 0 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 1 1 1 1 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 1 0 0 0 0 0 0 1 0 0 0 1 , b # 1 0 0 0 0 0 0 0 0 0 0 1 0 0 0 1 ; The DSP program initializes pointers to the top of the buffer: i3 = ^init_cmds; 13 = %init_cmds; and puts the first entry in the DSP’s transmit buffer so that it is available at the first SDOFS pulse: ax0 = dm(i3,m1); tx0 = ax0; The DSP’s transmit interrupt is enabled: imask = b#0001000000; |
Numéro de pièce similaire - AD73322L_17 |
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Description similaire - AD73322L_17 |
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