cop87l84bc National Semiconductor Corporation, cop87l84bc Datasheet - Page 23

• Manufacturer Part Number: cop87l84bc
• Description: 8-bit Cmos Otp Microcontrollers With 16k Memory, Comparators, And Can Interface
• Manufacturer: National Semiconductor Corporation

Functional Block Description of
the CAN Interface
This register is read/write.
Reserved Bit 7 is reserved and must be zero.
RID10..RID4 Receive Identifier bits (upper bits)
The RID10...RID4 bits are the upper 7 bits of the eleven bit
long Receive Identifier. If the Receive Identifier Acceptance
Filter (RIAF) bit (see CBUS register) is set to zero, bits 4 to
10 of the received identifier are compared with the mask bits
of RID4..RID10. If the corresponding bits match, the mes-
sage is accepted. If the RIAF bit is set to a one, the filter
function is disabled and all messages, independent of iden-
tifier, will be accepted.
CAN PRESCALER REGISTER (CSCAL) (Address
X’00B8)
This register is read/write.
CKS7..0 Prescaler divider select.
The resulting clock value is the CAN Prescaler clock.
CAN BUS TIMING REGISTER (CTIM) (00B9)
This register is read/write.
PPS2..PPS0 Propagation Segment, bits 2..0
The PPS2..PPS0 bits determine the length of the propaga-
tion delay in Prescaler clock cycles (PSC) per bit time. (For
a more detailed discussion of propagation delay and phase
segments, see SYNCHRONIZATION.)
PS2..PS0 Phase Segment 1, bits 2..0
The PS2..PS0 bits fix the number of Prescaler clock cycles
per bit time for phase segment 1 and phase segment 2. The
PS2..PS0 bits also set the synchronization Jump Width to a
value equal to the lesser of: 4 PSC, or the length of PS1/2
(Min: 4 l length of PS1/2).
LENGTH OF TIME SEGMENTS (See Figure 31 )
• The Synchronization Segment is 1 CAN Prescaler clock
• The Propagation Segment can be programmed (PPS) to
• Phase Segment 1 and Phase Segment 2 are program-
CKS7
PPS2
Bit 7
Bit 7
PS2
0
0
0
0
1
1
1
1
(PSC)
be 1,2...,8 PSC in length.
mable (PS) to be 1,2,..,8 PSC long.
PPS1
CKS6
TABLE 4. Synchronization Jump Width
PS1
0
0
1
1
0
0
1
1
PPS0
CKS5
PS0
0
1
0
1
0
1
0
1
PS2
CKS4
Segment
Length of
Phase
1 t
2 t
3 t
4 t
5 t
6 t
7 t
8 t
PS1
can
can
can
can
can
can
can
can
(Continued)
CKS3
1
PS0
⁄
2
CKS2
Synchronization
Reserved
Jump Width
1 t
2 t
3 t
4 t
4 t
4 t
4 t
4 t
CKS1
can
can
can
can
can
can
can
can
Reserved
Bit 0
CKS0
Bit 0
23
Note: (BTL settings at high speed; PSC = 0) Due to the on-chip delay from
CAN BUS CONTROL REGISTER (CBUS) (00BA)
Reserved This bit is reserved and must be zero.
RIAF
If the RIAF bit is set to zero, bits 4 to 10 of the received iden-
tifier are compared with the mask bits of RID4..RID10 and if
the corresponding bits match, the message is accepted. If
the RIAF bit is set to a one, the filter function is disabled and
all messages independent of the identifier will be accepted.
TxEN0, TxEN1 TxD Output Driver Enable
Bus synchronization of the device is done in the following
way:
If the output was disabled (TxEN1, TxEN0 = “0”) and either
TxEN1 or TxEN0, or both are set to 1, the device will not start
transmission or reception of a frame until eleven consecutive
“recessive” bits have been received. Resetting the TxEN1
and TxEN0 bits will disable the output drivers and the CAN
input comparator. All other CAN related registers and flags
will be unaffected. It is recommended that the user reset the
TxEN1 and TxEN0 bits before switching the device into the
HALT mode (the CAN receive wakeup will still work) in order
to reduce current consumption and to assure a proper resy-
chronization to the bus after exiting the HALT mode.
Note: A “bus off” condition will also cause Tx0 and Tx1 to be at TRI-STATE
RXREF1 Reference voltage applied to Rx1 if bit is set
RXREF0 Reference voltage applied to Rx0 if bit is set
FMOD
Setting the FMOD bit to “0” (default after power on reset) will
select the Standard Fault Confinement mode. In this mode
the device goes from “bus off” to “error active” after monitor-
ing 128*11 recessive bits (including bus idle) on the bus. This
mode has been implemented for compatibility with existing
solutions. Setting the FMOD bit to “1” will select the En-
hanced Fault Confinement mode. In this mode the device
goes from “bus off” to “error active” after monitoring 128
“good” messages, as indicated by the reception of 11 con-
secutive “recessive” bits including the End of Frame,
whereas the standard mode may time out after 128 x 11 re-
cessive bits (e.g., bus idle).
served
Bit 7
Re-
TxEN1
the rx-pins through the receive comparator (worst case assumption: 3
clocks delay * 2 (devices on the bus) + 1 tx delay) the user needs to set
the sample point to (2*3 + 1) i.e., 7 CKI clocks to ensure correct com-
munication on the bus under all circumstances. With prescaler settings
of 0 this is a given (i.e., no caution has to be applied).
Example: for 1 Mbit CTIM = b’10000100 (PSS = 5; PS1 = 2). Example
for 500 kbit CTIM = b’01011100 (PPS = 3; PS1 = 8). − all at 10 MHz
CKI and CSCAL = 0.
(independent of the values of the TxEN1 and TxEN0 bits).
0
0
1
1
RIAF
Fault Confinement Mode select
Receive identifier acceptance filter bit
TxEN1
TxEN0
TABLE 5. Output Drivers
0
1
0
1
TxEN0
Tx0, Tx1 TRI-STATE, CAN
input comparator disabled
Tx0 enabled
Tx1 enabled
Tx0 and Tx1 enabled
RxREF1
RxREF0
Output
served
Re-
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FMOD
Bit 0