ADJUSTMENT OF THE BUS CLOCK RATE
The MACCELERATE!750 offers a three level adjustment of the bus clock rate, that switches
the clock division factor for the CPU too, so that the processor is set always to a secure CPU
clock rate for the different available bus clock rates. System stability is ensured this way.
Secure operation at 55MHz bus clock rate was verified in tests with PowerMac models
7300, 7500, 7600, 8500 and 9500 as well as Tsunami mainboards in various tests. The
following combinations are available:
MACCELERATE!750-275
MACCELERATE!750-300
Bus speed:
45MHz
50MHz
55MHz
46.2MHz 50MHz
55MHz
Divider:
6:1
5.5:1
5:1
6.5:1
6:1
5.5:1
CPU clock rate:
270MHz
275MHz 275MHz
300.3MHz 300MHz
302.5MHz
Clock rate selector:
0
1
2
0
1
2
The clock selector is located in the lower right edge of the MACCELERATOR!750 PCB (refer
to picture 10). Use a small flat screw driver to adjust the clock rate selector to the desired
bus clock / CPU clock rate.
ADVICE:
Clock rate selector settings 7, 8 and 9 are not used and result in the same
selection as setting 1.
OVERCLOCKING THE MACCELERATE!750
The MACCELERATE!750 offers three additional clock rate selector settings for test purpo-
ses that are selected by setting 4, 5 and 6 of the clock rate selector after a overclock pro-
tection has been removed. The overclock protection is a track on the backside of the
MACCELERATE!750 PCB, that has to be cut to enable overclocking.
20
M
A
CCELERATE
!750 User manual
Picture 10.
The clock rate selector
