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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
348 of 808
NXP Semiconductors
UM10360
Chapter 16: LPC17xx CAN1/2
9.3 Central Miscellaneous Status Register (CANMSR - 0x4004 0008)
10. Global acceptance filter
This block provides lookup for received Identifiers (called Acceptance Filtering in CAN
terminology) for all the CAN Controllers. It includes a 512
×
32 (2 kB) RAM in which
software maintains one to five tables of Identifiers. This RAM can contain up to 1024
Standard Identifiers or 512 Extended Identifiers, or a mixture of both types.
11. Acceptance filter modes
The Acceptance Filter can be put into different modes by setting the according AccOff,
AccBP, and eFCAN bits in the Acceptance Filter Mode Register (
“Acceptance Filter Mode Register (AFMR - 0x4003 C000)”
). During each mode the
access to the Configuration Register and the ID Look-up table is handled differently.
[1]
The whole ID Look-up Table RAM is only word accessible.
[2]
During the Operating Mode of the Acceptance Filter the Look-up Table can be accessed only to disable or
enable Messages.
Table 319. Central Miscellaneous Status Register (CANMSR - address 0x4004 0008) bit
description
Bit
Symbol Description
Reset
Value
0
E1
When 1, one or both of the CAN1 Tx and Rx Error Counters has reached
the limit set in the CAN1EWL register (same as ES in CAN1GSR)
0
1
E2
When 1, one or both of the CAN2 Tx and Rx Error Counters has reached
the limit set in the CAN2EWL register (same as ES in CAN2GSR)
0
7:2
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
8
BS1
When 1, the CAN1 controller is currently involved in bus activities (same
as BS in CAN1GSR).
0
9
BS2
When 1, the CAN2 controller is currently involved in bus activities (same
as BS in CAN2GSR).
0
31:10 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
Table 320. Acceptance filter modes and access control
Acceptance
filter mode
Bit
AccOff
Bit
AccBP
Acceptance
filter state
ID Look-up
table
RAM
Acceptanc
e filter
config.
registers
CAN controller
message receive
interrupt
Off Mode
1
0
reset &
halted
r/w access
from CPU
r/w access
from CPU
no messages
accepted
Bypass
Mode
X
1
reset &
halted
r/w access
from CPU
r/w access
from CPU
all messages
accepted
Operating
Mode and
FullCAN
Mode
0
0
running
read only
from CPU
access from
Acceptance
filter only
hardware
acceptance filtering