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controller. If it finds an equal match, the AF signals the CAN controller to retain the message, and provides it with an ID Index
value to store in its the Receive Frame Status register register.
If the Acceptance Filter does not find a match in the appropriate individual Identifier table, it then searches the Identifier Range
table for the size of Identifier signalled by the CAN controller. If the AF finds a match to a range in the table, it similarly signals
the CAN controller to retain the message, and provides it with an ID Index value to store in its the Receive Frame Status register
register. If the Acceptance Filter does not find a match in either the individual or Range table for the size of Identifier received,
it signals the CAN controller to discard/ignore the received message.
ACCEPTANCE FILTER REGISTERS
Acceptance Filter Mode Register (AFMR - 0xE003 C000)
Table 145: Acceptance Filter Modes Register (AFMR - 0xE003 C000)
AFMR Name Function
1: if AccBP is 0, the Acceptance Filter is not operational. All Rx messages on all CAN buses are
0
AccOff
ignored.
1: all Rx messages are accepted on enabled CAN controllers. Software must set this bit before
modifying the contents of any of the registers described below, and before modifying the
1
AccBP
contents of Lookup Table RAM in any way other than setting or clearing Disable bits in Standard
Identifier entries. When both this bit and AccOff are 0, the Acceptance filter operates to screen
received CAN Identifiers.
1: the Acceptance Filter itself will take care of receiving and storing messages for selected
Standard ID values on selected CAN buses. See "FullCAN Mode" on page 176.
2
eFCAN
0: software must read all messages for all enabled IDs on all enabled CAN buses, from the
receiving CAN controllers.
Standard Frame Individual Start Address Register (SFF_sa - 0xE003 C004)
Table 146: Standard Frame Start Address Register (SFF_sa - 0xE003 C004)
SFF_sa Name Function
The start address of the table of individual Standard Identifiers in AF Lookup RAM. If the table
is empty, write the same value in this register and the SFF_GRP_sa register described below.
For compatibility with possible future devices, please write zeroes in bits 31:11 and 1:0 of this
10:2
register. If the eFCAN bit in the AFMR is 1, this value also indicates the size of the table of
Standard IDs which the Acceptance Filter will search and (if found) automatically store received
messages in Acceptance Filter RAM.
Standard Frame Group Start Address Register (SFF_GRP_sa - 0xE003 C008)
Table 147: Standard Frame Group Start Address Reg (SFF_GRP_sa - 0xE003 C008)
Name Function
SFF_GRP_sa
The start address of the table of grouped Standard Identifiers in AF Lookup RAM. If the table
is empty, write the same value in this register and the EFF_sa register described below. The
largest value that should be written to this register is 0x800, when only the Standard
11:2
Individual table is used, and the last word (address 0x7FC) in AF Lookup Table RAM is used.
For compatibility with possible future devices, please write zeroes in bits 31:12 and 1:0 of
this register.
CAN Controllers and Acceptance Filter
LPC2119/2129/2292/2294
173
Preliminary User Manual
Reset Value
1
0
0
Reset Value
0
Reset Value
0
January 08, 2004
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