OM11077 NXP Semiconductors, OM11077 Datasheet - Page 509

• Manufacturer Part Number: OM11077
• Description: MODULE DIMM LPC2478 ARM7
• Manufacturer: NXP Semiconductors

Specifications of OM11077

• Accessory Type: Module Card
• For Use With/related Products: ARM-57TS-LPC2478
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 568-4742

NXP Semiconductors
Table 454. Format of automatically stored Rx messages
UM10237_4
User manual
Address
0
+4
+8
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
F
F
Rx Data 4
Rx Data 8
R
T
R
17.1 FullCAN message layout
0000
The FF, RTR, and DLC fields are as described in
Since the FullCAN message object section of the Look-up table RAM can be accessed
both by the Acceptance Filter and the CPU, there is a method for insuring that no CPU
reads from FullCAN message object occurs while the Acceptance Filter hardware is
writing to that object.
For this purpose the Acceptance Filter uses a 3-state semaphore, encoded with the two
semaphore bits SEM1 and SEM0 (see
messages”) for each message object. This mechanism provides the CPU with information
about the current state of the Acceptance Filter activity in the FullCAN message object
section.
The semaphore operates in the following manner:
Table 455. FullCAN semaphore operation
Prior to writing the first data byte into a message object, the Acceptance Filter will write
the FrameInfo byte into the according buffer location with SEM[1:0] = 01.
After having written the last data byte into the message object, the Acceptance Filter will
update the semaphore bits by setting SEM[1:0] = 11.
Before reading a message object, the CPU should read SEM[1:0] to determine the current
state of the Acceptance Filter activity therein. If SEM[1:0] = 01, then the Acceptance Filter
is currently active in this message object. If SEM[1:0] = 11, then the message object is
available to be read.
Before the CPU begins reading from the message object, it should clear SEM[1:0] = 00.
When the CPU is finished reading, it can check SEM[1:0] again. At the time of this final
check, if SEM[1:0] = 01 or 11, then the Acceptance Filter has updated the message object
during the time when the CPU reads were taking place, and the CPU should discard the
data. If, on the other hand, SEM[1:0] = 00 as expected, then valid data has been
successfully read by the CPU.
Figure 18–82
read from the message are all from the same received message.
SEM1
0
1
0
SEM
[1:0]
SEM0
1
1
0
0000
Rx Data 3
Rx Data 7
shows how software should use the SEM field to ensure that all three words
activity
Acceptance Filter is updating the content
Acceptance Filter has finished updating the content
CPU is in process of reading from the Acceptance Filter
Rev. 04 — 26 August 2009
DLC
Table 18–454 “Format of automatically stored Rx
00000
Rx Data 2
Rx Data 6
Chapter 18: LPC24XX CAN controllers CAN1/2
Table
18–428.
ID.28 ... ID.18
8
7
Rx Data 1
Rx Data 5
6
UM10237
© NXP B.V. 2009. All rights reserved.
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