AD1845 DIRECT CONTROL REGISTER DEFINITIONS
Index Address Register (ADR1:0 = 0) ADR1:0
Index Address. These bits define the address of the AD1845 register accessed by the Indexed Data Register. These bits are read/write. IXA4 is not active in MODE1. Always write 0 to this bit when using the AD1845 in MODE1.
Transfer Request Disable. This bit, when set, causes DMA transfers to cease when the Interrupt Status (INT) bit of the Status Register is set. 0
Transfers Enabled During Interrupt. PDRQ and CDRQ pin outputs are generated uninhibited by interrupts. DMA Current Counter Register decrements with every sample period when either PEN or CEN are enabled. 1 Transfers Disabled By Interrupt. PDRQ and CDRQ pin outputs are generated only if INT bit is 0 (when either PEN or CEN, respectively are enabled). Any pending playback or capture requests are allowed to complete at the time when TRD is set. After pending requests complete, the data in the FIFO will be consumed at the sample rate. Subsequently, the midscale inputs will be internally generated for the DACs if the DACZ bit is set, otherwise, the previous valid sample will be repeated, and the ADC output buffer will contain the last valid output. Clearing the sticky INT bit (or the TRD bit) will cause the resumption of playback and/or capture requests (presuming PEN and/or CEN are enabled). The DMA Current Counter Register will not decrement while both the TRD bit is set and the INT bit is a one. No over run or under run error will be reported when transfers are disabled by INT. Mode Change Enable. This bit must be set whenever the current functional mode of the AD1845 is changed where noted in the Indirect Control Registers 8, 9, 28 and 29. MCE must be cleared at the completion of the desired register changes.
The DAC outputs are automatically muted when the MCE bit is set. After MCE is cleared, the DAC outputs will be restored to the state specified by the LDM and RDM mute bits. Both ADCs and DACs are automatically muted for 128 sample cycles after exiting the MCE state to allow the reference and all filters to settle. The ADCs will produce midscale values; the DACs’ analog output will be muted. All converters are internally operating during these 128 sample cycles, and the AD1845 will expect playback data and will generate (midscale) capture data. Note that the autocalibrate-in-progress (ACI) bit will be set on exiting from the MCE state regardless of whether or not ACAL was set. ACI will remain HI for these 128 sample cycles, allowing system software to poll this bit rather than count cycles. Special sequences must be followed if autocalibrate (ACAL) is set during mode change enable. See the “Autocalibration” section. INIT
AD1845 Initialization. This bit is set when the AD1845 cannot respond to parallel bus cycles. This bit is read-only.
Immediately after reset and once the AD1845 has left the INIT state, the initial value of this register will be “0100 0000 (40h).” During AD1845 initialization, this register cannot be written and always reads “1000 0000 (80h).” Indexed Data Register (ADR1:0 = 1) ADR1:0
Data 7 IXD7
Indexed Register Data. These bits contain the contents of the AD1845 register referenced by the Indexed Data Register.
During AD1845 initialization, this register cannot be written and always reads as “1000 0000 (80h).”