CHAPTER 31 CAUTIONS FOR WAIT
Preliminary User’s Manual U17260EJ3V1UD
618
31.2 Peripheral Hardware That Generates Wait
Table 31-1 lists the registers that issue a wait request when accessed by the CPU, and the number of CPU wait
clocks.
Table 31-1. Registers That Generate Wait and Number of CPU Wait Clocks
Peripheral
Hardware
Register
Access
Number of Wait Clocks
Serial interface
UART0
ASIS0
Read
1 clock (fixed)
Serial interface
UART6
ASIS6
Read
1 clock (fixed)
Serial interface
IIC0
IICS0
Read
1 clock (fixed)
ADM Write
ADS Write
ADPC Write
ADCR Read
1 to 5 clocks (when f
AD
= f
PRS
/2 is selected)
1 to 7 clocks (when f
AD
= f
PRS
/3 is selected)
1 to 9 clocks (when f
AD
= f
PRS
/4 is selected)
2 to 13 clocks (when f
AD
= f
PRS
/6 is selected)
2 to 17 clocks (when f
AD
= f
PRS
/8 is selected)
2 to 25 clocks (when f
AD
= f
PRS
/12 is selected)
A/D converter
The above number of clocks is when the same source clock is selected for f
CPU
and f
PRS
. The number of wait
clocks can be calculated by the following expression and under the following conditions.
<Calculating number of wait clocks>
•
Number of wait clocks = {(1/f
AD
)
×
2/(1/f
CPU
)} + 1
* Fraction is truncated if the number of wait clocks
≤
0.5 and rounded up if the number of wait clocks > 0.5.
f
AD
:
A/D conversion clock frequency (f
PRS
/2 to f
PRS
/12)
f
CPU
: CPU clock frequency
f
PRS
: Peripheral hardware clock frequency
f
XP
:
Main system clock frequency
<Conditions for maximum/minimum number of wait clocks>
•
Maximum number of times: Maximum speed of CPU (f
XP
), lowest speed of A/D conversion clock (f
PRS
/12)
•
Minimum number of times: Minimum speed of CPU (f
SUB
/2), highest speed of A/D conversion clock (f
PRS
/2)
Caution When the CPU is operating on the subsystem clock and the peripheral hardware clock is stopped,
do not access the registers listed above using an access method in which a wait request is issued.
Remark
The clock is the CPU clock (f
CPU
).
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