Application Considerations:
Although the device has a 4XXX PC 179 pin
R4700 or R4400 socket. The R4700 is closest
to the RM5260 whereas the R4400 is quite
different.
PGA compatible footprint, it is not a drop-in
replacement since the RM5260 has a different
clocking scheme. The RM5260 does not
generate the system clocks the same as the
R4400, R4600 and R4700. Instead, the system
clock is an input, which is multiplied up to the
pipeline rate. On the adapter, the Tclock and
Rclock pins are floating; not connected to
anything. SYNCout and IOout are connected to
ground to commit possible unconnected CMOS
inputs to a level. Depending on the system
configuration, accommodating the clocking
difference can be as simple as a few re-routing
jumpers or generating divisors of the original
MasterClock and the addition of some
phase-skewing buffers to emulate the Rclock
and Tclock system clocks. In addition, the boot
time mode bit serial stream needs to be
scrutinized before plugging in a RM5260 into an
Figure 2 is an example of what had to be done
to an Algorithmics P4000i (IDT79S460) Single
Board Computer which was originally configured
for an R4700 with a 50 MHz input clock (100
MHz pipeline) and a divide by 2 output clock (50
MHz bus rate). With three wire jumpers, the
ACT5260PC-P10-POD was up and running with
no changes to the boot and monitor PROM or
any recompilation of application programs. In
this case, the R4700's modebit stream
happened to be compatible, where a board
jumper used to change the output clocks (Tclock
and Rclock) from divide by 2 to divide by 3 had
the effect of changing the Pclock multiplier from
2 to 3, upping the pipeline rate up to 150 Mhz
without changing the board oscillator.
R4700
ACT5260PC
Oscillator
Oscillator
50MHz
50MHz
From
To
Figure 2 – Setup Example
3
Aeroflex Circuit Technology
SCD5260PC REV A 9/15/97 Plainview NY (516) 694-6700
AEROFLEX [ AEROFLEX CIRCUIT TECHNOLOGY ]
