MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
19-46 Freescale Semiconductor
19.4.1.1 Assumptions/Requirements Regarding the External Device
The external device exchanges command and result data with the eQADC through the eQADC SSI
interface. This section explains the minimum requirements an external device has to meet to properly
interface with the eQADC. Some assumptions about the architecture of the external device are also
described.
19.4.1.1.1 eQADC SSI Protocol Support
The external device must fully support the eQADC SSI protocol as specified in Section 19.4.8, “eQADC
Synchronous Serial Interface (SSI) Submodule,” section of this document. Support for the abort feature is
optional. When aborts are not supported, all command messages bound for an external command buffer
must have the ABORT_ST bit negated - see Section , “ Command Message Format for External Device
Operation.”
19.4.1.1.2 Number of Command Buffers and Result Buffers
The external device should have a minimum of one and a maximum of two command buffers to store
command data sent from the eQADC. If more than two command buffers are implemented in the external
device, they are not recognized by the eQADC as valid destinations for commands. In this document, the
two valid external command buffers are referred to as command buffer 2 and command buffer 3 (the two
on-chip ADCs being command buffer 0 and 1). The external device decides to which external command
buffer a command should go by decoding the upper bit (BN bit) of the ADC command - see Section ,
“ Command Message Format for External Device Operation.” An external device that only implements
one command buffer can ignore the BN bit.
The limit of two command buffers does not limit the number of result buffers in the slave device.
19.4.1.1.3 Command Execution and Result Return
Commands sent to a specific external command buffer should be executed in the order they were received.
Results generated by the execution of commands in an external command buffer should be returned in the
order that the command buffer received these commands.
19.4.1.1.4 Null and Result Messages
The external device must be capable of correctly processing null messages as specified in the
Section 19.3.2.2, “eQADC Null Message Send Format Register (EQADC_NMSFR).”
In case no valid result data is available to be sent to the eQADC, the external device must send data in the
format specified in Section , “ Null Message Format for External Device Operation.”
In case valid result data is available to sent to the eQADC, the external device must send data in the format
specified in Section , “ Result Message Format for External Device Operation.”
The BUSY0/1 fields of all messages sent from the external device to the eQADC must be correctly
encoded according to the latest information on the fullness state of the command buffers. For example, if
external command buffer 2 is empty before the end of the current serial transmission and if at the end of
this transmission the external device receives a command to command buffer 2, then the BUSY0 field, that
is to be sent to the eQADC on the next serial transmission, should be encoded assuming that the external
command buffer has one entry.
To Next Page
Loading...