Clock Select Header (W1) - Motorola M68MPB16Y1 User Manual

2.2.1

Clock Select Header (W1)

Jumper header W1 connects the MCU external clock (EXTAL) pin to either an
on-board or external (target-system) clock source. The drawing below shows the
factory configuration: a fabricated jumper on pins 1 and 2. This configuration
selects the MPB on-board clock source; crystal oscillator in the Y1 socket. (This
crystal provides for operation at the maximum rate the MCU allows via the
internal phase-locked loop or direct clock input.)
If you install the MPB in the active probe or directly on a target system, and use
the target system clock as the MPB clock, move the fabricated jumper to W1 pins
2 and 3. This connects the MCU EXTAL pin to the MAPI bus input pin. The
frequency of the external clock signal can be from 32 KHz to 16.78 MHz (or to
the maximum the MCU allows).
M68MPB16Y1UM/D
You cannot drive the MPB clock circuit from an external source
(target system) with a discrete crystal. If you use a target system
clock source to drive the MPB clock circuit, always use a logic-
driven clock such as a hybrid oscillator.
HARDWARE PREPARATION AND INSTALLATION
W1
1
2
3
NOTE
2-5