INITIALIZATION AND SYSTEM REQUIREMENTS
12-35
12
12.6.3
V
CC5
Pin Requirements
In 3.3 V-only systems and systems that drive the i960 Jx processor pins from 3.3 V logic, connect
the V
CC5
pin directly to the 3.3 V V
CC
plane.
In mixed voltage systems that drive the i960 Jx Processor inputs in excess of 3.3 V, the V
CC5
pin
must be connected to the system’s 5 V supply. To limit current flow into the V
CC5
pin, there is a limit
to the voltage differential between the V
CC5
pin and other V
CC
pins. The voltage differential (V
DIFF
)
between the 80960Jx V
CC5
pin and its 3.3 V V
CC
pins should never exceed 2.25 V. This limit applies
to power up, power down and steady-state operation. Refer to
section 1.4, “Related Documents”
(pg. 1-10)
. Further information can be found for the V
CC5
pin requirements in these documents.
If the voltage difference requirements cannot be meet due to system design limitations, an alternate
solution may be employed. As shown in Figure, a minimum of a 100
Ω
series resistor may be used
to limit the current into the V
CC5
pin. This resistor ensures that current drawn by the V
CC5
pin does
not exceed the maximum rating for this pin.
Figure 12-9. V
CC5
Current-Limiting Resistor
This resistor is not necessary in systems that can guarantee the V
DIFF
specification.
12.6.4
Power and Ground Planes
Power and ground planes are recommended to be used in i960 Jx processor systems to minimize noise.
Justification for these power and ground planes is the same as for multiple V
SS
and V
CC
pins. Power
and ground lines have inherent inductance and capacitance; therefore, an impedance Z=(L/C)
1/2
.
Total characteristic impedance for the power supply can be reduced by adding more lines. This effect
is illustrated in
Figure 12-10
, which shows that two lines in parallel have half the impedance of one.
Ideally, a plane — an infinite number of parallel lines — results in the lowest impedance. Fabricate
power and ground planes with a 1 oz. copper for outer layers and 0.5 oz. copper for inner layers.
All power and ground pins must be connected to the planes. Ideally, the i960 Jx processor should
be located at the center of the board to take full advantage of these planes, simplify layout and
reduce noise.
5 V V
CC
V
CC5
Pin
100
Ω
(±5%, 0.5 W)
(BOARD PLANE)
Summary of Contents for i960 Jx
Page 1: ...Release Date December 1997 Order Number 272483 002 i960 Jx Microprocessor Developer s Manual ...
Page 24: ......
Page 25: ...1 INTRODUCTION ...
Page 26: ......
Page 35: ...2 DATA TYPES AND MEMORY ADDRESSING MODES ...
Page 36: ......
Page 46: ......
Page 47: ...3 PROGRAMMING ENVIRONMENT ...
Page 48: ......
Page 73: ...4 CACHE AND ON CHIP DATA RAM ...
Page 74: ......
Page 85: ...5 INSTRUCTION SET OVERVIEW ...
Page 86: ......
Page 111: ...6 INSTRUCTION SET REFERENCE ...
Page 112: ......
Page 233: ...7 PROCEDURE CALLS ...
Page 234: ......
Page 256: ......
Page 257: ...8 FAULTS ...
Page 258: ......
Page 291: ...9 TRACING AND DEBUGGING ...
Page 292: ......
Page 309: ...10 TIMERS ...
Page 310: ......
Page 324: ......
Page 325: ...11 INTERRUPTS ...
Page 326: ......
Page 369: ...12 INITIALIZATION AND SYSTEM REQUIREMENTS ...
Page 370: ......
Page 412: ......
Page 413: ...13 MEMORY CONFIGURATION ...
Page 414: ......
Page 429: ...14 EXTERNAL BUS ...
Page 430: ......
Page 468: ......
Page 469: ...15 TEST FEATURES ...
Page 470: ......
Page 493: ...A CONSIDERATIONS FOR WRITING PORTABLE CODE ...
Page 494: ......
Page 502: ......
Page 503: ...B OPCODES AND EXECUTION TIMES ...
Page 504: ......
Page 515: ...C MACHINE LEVEL INSTRUCTION FORMATS ...
Page 516: ......
Page 523: ...D REGISTER AND DATA STRUCTURES ...
Page 524: ......
Page 550: ......
Page 551: ...GLOSSARY ...
Page 552: ......
Page 561: ...INDEX ...
Page 562: ......
Page 578: ......