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Chapter 14
FCAN Interface Function
Preliminary User’s Manual U15839EE1V0UM00
(2)
CAN main clock select register (CGCS)
The CGCS register controls the internal memory access clock (f
MEM
), which is used as main clock
for each CAN module, as well as the global time system clock (f
GTS
), used for the time stamp func-
tion and event generation. (For details refer to chapter 14.2.3 “Clock structure” on page 438.
This register can be read/written in 1-bit, 8-bit and16-bit units.
Figure 14-9:
CAN Main Clock Select Register (CGSC) (1/2)
Note: The address of an interrupt pending register is calculated according to the following formula:
effective address = P address offset
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Address
Offset
Note
Initial
value
CGCS CGTS7 CGTS6 CGTS5 CGTS4 CGTS3 CGTS2 CGTS1 CGTS0 GTSC0 GTSC0
0
MCS MCP3 MCP2 MCP1 MCP0
1014H
7F05H
Bit Position
Bit Name
Function
15 to 8
CGTS7 to
CGTS0
Specifies the 8-bit prescaler compare value for the global time system clock (f
GTS
)
(ref. to Fig. 9-11).
Remark:
The global time system clock is the source clock for the 16-bit timer used
for the time stamp functionality. This clock is common for all CAN modules.
7, 6
GTCS1,
GTCS0
Selects the global time system basic clock (f
GTS1
) from the memory clock (f
MEM
) (ref.
to Fig. 9-11).
4
MCS
Selects input clock for the memory access clock prescaler (f
MEM1
) (ref. to Fig. 9-10).
0: f
MEM1
= internal system clock (f
CPU
)
1: f
MEM1
= external clock input (f
EXT
)
Note
Note: V850E/CA2 doesn’t offer an external clock f
MEM
supply pin. Therefore, the
MCS must not be set at any time.
CGTS7 to CGTS0
(k)
Prescaler
(k + 1)
Global Time System Clock
f
GTS
= f
GTS1
/ (k + 1)
0
1
f
GTS
= f
GTS1
1
2
f
GTS
= f
GTS1
/ 2
2
3
f
GTS
= f
GTS1
/ 3
·
·
·
·
·
·
·
·
·
255
256
f
GTS
= f
GTS1
/ 256
GTCS1
GTCS0
Global Time System Basic Clock (f
GTS1
)
0
0
f
GTS1
= f
MEM
/ 2
0
1
f
GTS1
= f
MEM
/ 4
1
0
f
GTS1
= f
MEM
/ 8
1
1
f
GTS1
= f
MEM
/ 16
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