MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor 19-55
19.4.1.2.2 Message Formats for External Device Operation
This section describes the command messages, data messages, and null messages formats used for external
device operation.
Command Message Format for External Device Operation
Figure 19-31 describes the command message format for external device operation. Command message
formats for on-chip operation and for external device operation share the same CFIFO header format.
However, there are no limitations regarding the format an ADC Command used to communicate to an
arbitrary external device. Only the upper bit of an ADC Command has a fixed format (BN field) to indicate
to the FIFO control unit/external device to which external command buffer the corresponding command
should be sent. The remaining 25 bits can be anything decodable by the external device. Only the ADC
command portion of a command message is transferred to the external device.
Table 19-39. Correspondence between Analog Voltages and Digital Values
1, 2
1
V
REF
=V
RH
-V
RL
=5.12V. Resulting in one 12-bit count (lsb) =1.25mV.
2
The two’s complement representation is used to express negative values.
Voltage Level on
Channel
(V)
Corresponding 12-bit
Conversion Result
Returned by the ADC
16-bit Result
Sent to RFIFOs
(FMT=0)
3
3
Assuming uncalibrated conversion results.
16-bit Result
Sent to RFIFOs
(FMT=1)
3
Single-Ended
Conversions
5.12 0xFFF 0x3FFC 0x1FFC
5.12 – lsb 0xFFF 0x3FFC 0x1FFC
... ... ... ...
2.56 0x800 0x2000 0x0000
... ... ... ...
1 lsb 0x001 0x0004 0xE004
0 0x000 0x0000 0xE000
Differential
Conversions
2.56 0xFFF 0x3FFC 0x1FFC
2.56 – lsb 0xFFF 0x3FFC 0x1FFC
... ... ... ...
0 0x800 0x2000 0x0000
... ... ... ...
-2.56 + lsb 0x001 0x0004 0xE004
-2.56 0x000 0x0000 0xE000
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