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GR716-DS-UM, May 2019, Version 1.29
204
www.cobham.com/gaisler
GR716
24.2
Operation
24.2.1 Interfaces
The internal interface on the on-chip bus towards the core is a common AMBA APB slave for data
access, configuration and status monitoring, used by both the ADC interface and the DAC interface.
The ADC address output and the DAC address output signals are shared on the external interface.
The address signals are possible to use as general purpose input output channels. This is only realized
when the address signals are not used by either ADC or DAC.
The ADC data input and the DAC data output signals are shared on the external interface. The data
input and output signals are possible to use as general purpose input output channels. This is only
realized when the data signals are not used by either ADC or DAC.
Each general purpose input output channel shall be individually programmed as input or output. This
applies to both the address bus and the data bus. The default reset configuration for each general pur-
pose input output channel is as input. The default reset value each general purpose input output chan-
nel is logical zero.
Note that protection toward spurious pulse commands during power up shall be mitigated as far as
possible by means of I/O cell selection from the target technology.
24.2.2 Analogue to digital conversion
The ADC interface supports 8 and 16 bit wide input data.
The ADC interface provides an 8-bit address output, shared with the DAC interface. Note that the
address timing is independent of the acquisition timing.
The ADC interface shall provide the following control signals:
•
Chip Select
•
Read/Convert
•
Ready
The timing of the control signals is made up of two phases:
•
Start Conversion
•
Read Result
The Start Conversion phase is initiated by one of the following sources, provided that no other con-
version is ongoing:
•
Event on one of three separate trigger inputs
•
Write access to the AMBA APB slave interface
Note that the trigger inputs can be connected to internal or external sources to the ASIC incorporating
the core. Note that any of the trigger inputs can be connected to a timer to facilitate cyclic acquisition.
The selection of the trigger source is programmable. The trigger inputs is programmable in terms of:
Rising edge or Falling edge. Triggering events are ignored if ADC or DAC conversion is in progress.
The transition between the two phases is controlled by the Ready signal. The Ready input signal is
programmable in terms of: Rising edge or Falling edge. The Ready input signaling is protected by
means of a programmable time-out period, to assure that every conversion terminates. It is also possi-
ble to perform an ADC conversion without the use of the Ready signal, by means of a programmable
conversion time duration. This can be seen as an open-loop conversion.
The Chip Select output signal is programmable in terms of:
•
Polarity
•
Number of assertions during a conversion, either