ARM ARM7TDMI - Page 22

Open Access
Circuit Descriptions
3-6
ARM Development Board (ARM7TDMI Version)
Hardware Reference Guide
ARM DUI 0017C
Unused clock signals
Two clock signals are not used NISACLK1 and B_CLK8. These are available as monitor
points (V1 and V2), as shown in
A.2 Top-level Diagram on page A-3.
Clock frequencies
The frequency of SYSCLK and SYSCLK2X can be controlled by three inputs
(CLKSEL[2:0]). A switch (S1) is used to control these select lines via a PAL (U2), which is
used to prevent inappropriate clock frequencies being selected.
Ref Position Name Option Description
S1 1 SEL0 on/off see table below
2 SEL1 on/off see table below
3 SEL2 on/off see table below
4 SEL3 on/off see table below
Table 3-1: S1
Switch position Frequency (MHz
SEL3 SEL2 SEL1 SEL0 SYSCLK SYSCLK2X
on on on on 4 8
on on on off 8 16
on on off on 16 32
on on off off 20 40
Table 3-2: Switch positions
hrg.book Page 6 Wednesday, July 22, 1998 9:18 AM