NEC V850E/CA1 ATOMIC, Preliminary User'S Manual

Page: 397 / 601

397
Chapter 13 FCAN Interface Function
Preliminary User’s Manual U14913EE1V0UM00
(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 13.2.3 Clock structure)
These register can be read/written in 1-bit, 8-bit and16-bit units.
Figure 13-9: 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 814H 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. 13-11).
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 mod-
ules.
7, 6 GTCS1,
GTCS0
Selects the global time system basic clock (f
GTS1
) from the memory clock (f
MEM
) (ref.
to Fig. 13-11).
4 MCS Selects input clock for the memory access clock prescaler (f
MEM1
) (ref. to Fig. 13-10).
0: f
MEM1
= internal system clock (f
CPU
)
1: f
MEM1
= external clock input (f
EXT
)
Note
Note: If the external clock input is selected and f
MEM
= f
MEM1
is selected (MCP3 to
MCP0 = 0000B), the duty cycle of the external clock f
EXT
must be 50%.
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