Clock Switching - Oki Dr.63514 User Manual

Chapter 2. Functions

2.8 Clock Switching

The emulator offers the choice of internal or external clock signals to the XT (low-speed) and OSC
(high-speed) pins on the evaluation chip. These clocks can be selected from the following: the Dr.63514
clock and the clocks input to the USR.TXT and USR.OSC pins on the user cable.
Low-speed (XT)
High-speed (OSC)
The microcontroller's time-base counter always uses the XT input to generate clock signals for the
onboard peripherals. Its CPU, however, offers a choice of clock speeds: XT or OSC.
Using the faster (OSC) clock signal, however, introduces the risk of losing synchronization with the lower
(XT) during single-step emulation or in the course of repeated breaks during real-time emulation.
Results from timers and other onboard peripherals can therefore differ from those obtained during
continuous execution with real-time emulation.
Internal high-speed clock
2MHz
150KΩ
USR.OSC
(User cable)
150KΩ
USR.XT
(User cable)
VDD
operational
amplifier
5.1KΩ
5.1KΩ
Internal low-speed clock
65.536kHz
2-36
Internal 5V
power supply
+5V
External
high-speed
clock
+
-
MAX901
+5V
External
low-speed
+
clock
-
MAX901
+
-
Figure 2-17 Clock Circuits
Internal (32.768kHz)
External (user cable USR.XT pin)
Internal (2MHz)
External (user cable USR.OSC pin)
High-speed
OSC clock
OSC.SEL
IN
EXT
XT.SEL
IN
1/2
EXT
to OSC pin on
evaluation chip
+5V
OSC.OUT
(User cable)
HC541
+5V
XT.OUT
(User cable)
HC541
Low-speed
to XT pin on
XT clock
evaluation chip