Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
Freescale Semiconductor
18-59
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 18.3.2.1, “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 18.3.2.2, “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.
Table 18-42. Command BUFFER
n
BUSY Status
1
BUSY
n
[0:1]
Meaning
0b00
Send available commands—command buffer is empty
0b01
Send available commands
0b10
Send available commands
0b11
Do not send commands
1
After reset, the eQADC always assumes that the external command buffers are full and cannot
receive commands.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
CONTENTS OF EQADC_NMSFR REGISTER
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
CONTENTS OF EQADC_NMSFR REGISTER
Figure 18-33. Null Message Send Format for External Device Operation
Summary of Contents for MPC5565
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