GT-64260A Design Guide
Doc. No. MV-S300165-00, Rev. A
CONFIDENTIAL
Copyright © 2002 Marvell
Page 24
Document Classification: Proprietary Information
May 21, 2002, Preliminary
The bus keeper can supply up to ~50uA. This means if there is a Pull-up (e.g.,
10K-Ohm
) and the last value was
Low ('0'), the Pull-up will start pulling the signal high but the maximum current is 50 uA =>.
V(signal) = V(io) - [R(pull up) * I(maximum)] = 2.5 - [10000 * 0.00005]
V(signal) = 2V.
Note
IBM recommends using a 5K Ohm Pull-up that pulls the signal to 2.25V.
When the signal reaches the 'keeper' threshold voltage, the keeper drives the signals high and the signal voltage
reaches the V(IO) value.
A similar calculation can be used for the pull down with keeper. In this case with 10K Ohm V(signal) = 0.5V (or
0.25V for 5K Ohm). When the signal reaches to the 'keeper' threshold voltage, the keeper starts driving the signals
low and the signal voltage reaches the GND value.
Note
For more information, see the IBM datasheet.
3.5.5 PPC750FX Data Bus Parking
The GT-64260A internal 60x arbiter supports data bus parking.
See the GT-64260A errata and restriction document errata "FEr #CPU-1 Multiple data bus masters with IBM
PPC750CX/e CPUs". This errata is also applicable to PPC750FX DD1.x Revisions. The dd2.0 Revision and
higher will support data bus parking.
Note
PPC750FX first production revision is DD2.1. It is the revision that supports the data bus parking. Previous
revisions are defined as prototypes.
3.6
Multi-GT or Multi-slave Modes
It is possible to connect up to four GT-64260A or other 60x-bus compliant slave devices to the 60x bus without the
need for any glue logic.This capability (referred to as "Multi-GT" mode) adds significant system design flexibility.
Multiple GT-64260A is enabled by setting AD[9] to ’1’ at reset.
describes the Multi-GT system architecture.
Note
Each GT-64260A in the figure can be removed or replaced by another 60x compatible slave.