Peripheral Hardware That Generates Wait - NEC 78K0 Series User Manual

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
Serial interface ASIS0
UART0
Serial interface ASIS6
UART6
Serial interface IICS0
IIC0
A/D converter ADM
ADS
ADPC
ADCR
The above number of clocks is when the same source clock is selected for f
clocks can be calculated by the following expression and under the following conditions.
<Calculating number of wait clocks>
• Number of wait clocks = {(1/f
* Fraction is truncated if the number of wait clocks ≤ 0.5 and rounded up if the number of wait clocks > 0.5.
f :
AD
f
CPU
f
PRS
f :
XP
<Conditions for maximum/minimum number of wait clocks>
• Maximum number of times: Maximum speed of CPU (f
• Minimum number of times: Minimum speed of CPU (f
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
618
CHAPTER 31 CAUTIONS FOR WAIT
Register
Read
Read
Read
Write
Write
Write
Read
) × 2/(1/f
AD
A/D conversion clock frequency (f
: CPU clock frequency
: Peripheral hardware clock frequency
Main system clock frequency
).
CPU
Preliminary User's Manual U17260EJ3V1UD
Access
1 clock (fixed)
1 clock (fixed)
1 clock (fixed)
1 to 5 clocks (when f
1 to 7 clocks (when f
1 to 9 clocks (when f
2 to 13 clocks (when f
2 to 17 clocks (when f
2 to 25 clocks (when f
)} + 1
CPU
/2 to f /12)
PRS PRS
), lowest speed of A/D conversion clock (f
XP
/2), highest speed of A/D conversion clock (f
SUB
Number of Wait Clocks
= f /2 is selected)
AD PRS
= f /3 is selected)
AD PRS
= f /4 is selected)
AD PRS
= f /6 is selected)
AD PRS
= f /8 is selected)
AD PRS
= f /12 is selected)
AD PRS
and f . The number of wait
CPU PRS
PRS
PRS
/12)
/2)