Oki Dr.63514, User Manual, Page: 57 / 101

Chapter 2. Functions
2-36
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) Internal (32.768kHz)
External (user cable USR.XT pin)
High-speed (OSC) Internal (2MHz)
External (user cable USR.OSC pin)
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.
MAX901
MAX901
150K
Ω
150K
Ω
External
low-speed
clock
USR.OSC
(User cable)
USR.XT
(User cable)
High-speed
OSC clock
to OSC pin on
evaluation chip
to XT pin on
evaluation chip
OSC.OUT
(User cable)
XT.OUT
(User cable)
Low-speed
XT clock
Internal high-speed clock
Internal 5V
power supply
External
high-speed
clock
OSC.SEL
IN
EXT
XT.SEL
IN
EXT
2MHz
65.536kHz
1/2
VDD
+
-
operational
amplifier
+
-
+5V
+
-
+5V
HC541
+5V
HC541
+5V
Internal low-speed clock
5.1K
Ω
5.1K
Ω
Figure 2-17 Clock Circuits