4524 Datasheet, PDF (73/161 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4524 Group
(1) Main clock generating circuit (f(XIN))
The ceramic resonator or RC oscillation can be used for the main
clock of this MCU.
After system is released from reset, the MCU starts operation by
the clock output from the on-chip oscillator which is the internal os-
cillator.
When the ceramic resonator is used, execute the CMCK instruc-
tion. When the RC oscillation is used, execute the CRCK
instruction. The oscillation circuit by the CMCK or CRCK instruction
is valid only at once. The oscillation circuit corresponding to the first
executed one of these two instructions is valid. Other oscillation cir-
cuit and the on-chip oscillator stop.
Execute the CMCK or the CRCK instruction in the initial setting routine
of program (executing it in address 0 in page 0 is recommended).
Also, when the CMCK or the CRCK instruction is not executed in pro-
gram, this MCU operates by the on-chip oscillator.
(2) On-chip oscillator operation
When the MCU operates by the on-chip oscillator as the main clock
(f(XIN)) without using the ceramic resonator or the RC oscillation,
connect XIN pin to VSS and leave XOUT pin open (Figure 60).
The clock frequency of the on-chip oscillator depends on the supply
voltage and the operation temperature range.
Be careful that margin of frequencies when designing application
products.
(3) Ceramic resonator
When the ceramic resonator is used as the main clock (f(XIN)), con-
nect the ceramic resonator and the external circuit to pins XIN and
XOUT at the shortest distance. Then, execute the CMCK instruction.
A feedback resistor is built in between pins XIN and XOUT (Figure
61).
(4) RC oscillation
When the RC oscillation is used as the main clock (f(XIN)), connect
the XIN pin to the external circuit of resistor R and the capacitor C
at the shortest distance and leave XOUT pin open. Then, execute
the CRCK instruction (Figure 62).
The frequency is affected by a capacitor, a resistor and a micro-
computer. So, set the constants within the range of the frequency
limits.
Reset
On-chip oscillator
operation
CMCK instruction
CRCK instruction
• Ceramic resonator valid • RC oscillation valid
• On-chip oscillator stop • On-chip oscillator stop
• RC oscillation stop
• Ceramic resonator stop
Fig. 59 Switch to ceramic oscillation/RC oscillation
M34524
XIN
XOUT
* Do not use the CMCK instruction
and CRCK instruction in program.
Fig. 60 Handling of XIN and XOUT when operating on-chip oscillator
XIN
CI N
M34524
* Execute the CMCK instruc-
tion in program.
XOUT
Note: Externally connect a damping
resistor Rd depending on the
Rd
oscillation frequency.
(A feedback resistor is built-in.)
Use the resonator manu-
COUT
facturer’s recommended value
because constants such as ca-
pacitance depend on the
resonator.
Fig. 61 Ceramic resonator external circuit
M34524
* ^{Execute the CRCK}
R
XIN
XOUT
instruction in program.
C
Fig. 62 External RC oscillation circuit
Rev.2.00 Jul 27, 2004 page 73 of 159
REJ03B0091-0200Z