MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
19-58
Freescale Semiconductor
Null Message Format for External Device Operation
Null messages are only transferred through the serial interface to allow results and unsolicited control data,
like the status of the external command buffers, to return when there are no more commands pending to
transfer. Null messages are only transmitted when serial transmissions from the eQADC SSI are enabled
(see ESSIE field in
Section 19.3.2.1, “eQADC Module Configuration Register (EQADC_MCR)
when one of the following conditions apply:
1. There are no triggered CFIFOs with commands bound for external command buffers.
2. There are triggered CFIFOs with commands bound for external command buffers but the external
buffers are full. The eQADC detected returning BUSY
n
fields indicating “Do not send
commands.”
illustrates the null message send format. When the eQADC transfers a null message, it
directly shifts out the 26-bit data content inside the
Section 19.3.2.2, “eQADC Null Message Send Format
.” The register must be programmed with the null message send format of the
external device.
illustrates the null message receive format. It has the same fields found in a result message
with the exception that the ADC result is not used. Refer to
Section , “ Result Message Format for External
,” for more information. The MESSAGE_TAG field must be set to the null message tag
(0b1000). The eQADC does not store into an RFIFO any incoming message with a null message tag.
12–15
BUSYn
[0:1]
BUSY status. The BUSY fields indicate if the external device can receive more
commands.
shows how these two bits are encoded. When an external
device cannot accept any more new commands, it must set BUSYn to a value indicating
“Do not send commands” in the returning message. The BUSY fields of values 0b10 and
0b10 can be freely encoded by the external device to allow visibility of the status of the
external command buffers for debug. As an example, they could indicate the number of
entries in an external command buffer.
16–31
ADC_RESULT
[0:15]
ADC RESULT Field. The result data received from the external device or on-chip ADC.
This can be the result of a conversion command, data requested via a read configuration
command, or time stamp value. The ADC_RESULT of any incoming message with a null
message tag will be ignored. When the MESSAGE_TAG is for an RFIFO, the eQADC
extracts the 16-bit ADC_RESULT from the raw message and stores it into the
appropriate RFIFO.
Table 19-42. Command BUFFERn BUSY Status
1
1
After reset, the eQADC always assumes that the external command buffers are full and cannot
receive commands.
BUSYn[0:1]
Meaning
0b00
Send available commands—command buffer is empty
0b01
Send available commands
0b10
Send available commands
0b11
Do not send commands
Table 19-41. Result Message Format for External Device Operation (Continued)
Bits
Name
Description
Summary of Contents for MPC5553
Page 5: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 2 Freescale Semiconductor...
Page 21: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 xvi Freescale Semiconductor...
Page 47: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 1 26 Freescale Semiconductor...
Page 163: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 4 20 Freescale Semiconductor...
Page 179: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 5 16 Freescale Semiconductor...
Page 561: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 13 38 Freescale Semiconductor...
Page 615: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 14 54 Freescale Semiconductor...
Page 707: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 17 68 Freescale Semiconductor...
Page 755: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 18 48 Freescale Semiconductor...
Page 873: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 19 118 Freescale Semiconductor...
Page 984: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 Freescale Semiconductor 21 41...
Page 985: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 21 42 Freescale Semiconductor...
Page 1019: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 22 34 Freescale Semiconductor...
Page 1129: ...MPC5553 MPC5554 Microcontroller Reference Manual Rev 5 25 90 Freescale Semiconductor...