GT-64260A Design Guide
Doc. No. MV-S300165-00, Rev. A
CONFIDENTIAL
Copyright © 2002 Marvell
Page 22
Document Classification: Proprietary Information
May 21, 2002, Preliminary
Note
Make sure that all the Reset configuration strapping required by the GT-64260A with serial ROM
initialization are pulled to the correct values (the same value configured in the serial initialization). For
more information, see the GT-64260A datasheet’s "Reset Configuration" section.
3.5.2 MPC7410, MPC745x and PPC750CX/e Bus Voltage
The MPC7410, MPC745x and PPC750CX/e only supports 1.8V and 2.5V bus voltages (except for the 3.3V ver-
sion of the MPC7410). Alternatively, the GT-64260A supports 2.5V and 3.3V CPU interface voltages.
Therefore, when using one of these CPUs, it must be configured to work in 2.5V on the CPU bus by configuring
the CPU’s BVSEL pin to the correct value at reset. In addition, the GT-64260A’s CPU interface must be configured
to 2.5V at reset by setting AD31 to ’0’.
Note
AD31 must be pulled to the correct value at reset even when the serial ROM is enabled. This means the
CPU interface voltage value (AD[31]) and the serial initialization value (AD[0]) must be the same.
3.5.3 MPC745x Extended Pins
The MPC745x CPU supports a 32-bit addressing mode and a 36-bit extended addressing modes. When extended
physical addressing is disabled, the MPC745x drives the four most significant bits to zeroes.
Note
The four most significant bits are still sampled and must be actively pulled to zero if they are not being
used in a system.
The MPC745x Address and address parity buses must be connected to the GT-64260A as follows:
•
Pull MPC745x A[0:3] to b’0000’.
•
Connect MPC745x A[4:35] to GT-64260A A[0:31].
•
Pull MPC745x AP[0] to b’1’.
•
Connect MPC745x AP[1:4] to GT-64260A AP[0:3].
Additionally, the MPC745x microprocessor supports a 4-bit DTI index, with a maximum value of DTI[0:3] = b’1111’.
Therefore, the DTI bus must be connected to the GT-64260A as follows:
•
Pull MPC745x DTI[0] to b’0’.
•
Connect MPC745x DTI[1:3] to GT-64260A DTI[0:2].
3.5.4 PPC750FX Level Protection
The PPC750FX CPU implements signal 'keepers' on some of its IO pads. The keeper can be viewed as two cross-
coupled inverters. (See
). Inverter B is extremely weak. It can supply a maximum of ~50uA.