12-19
GTL+ INTERFACE SPECIFICATION
12.2.3.2.
MINIMUM SETUP AND HOLD TIMES
Setup time for GTL+ (T
SU
) is defined as:
The minimum time from the input signal pin crossing of V
REF
to the clock
pin of the receiver crossing the 1.5 V level, which guarantees that the input
buffer has captured new data at the input pin, given an infinite hold time.
Strictly speaking, setup time must be determined when the input barely meets minimum hold
time (see definition of hold time below). However, for current GTL+ systems, hold time should
be met well beyond the minimum required in cases where setup is critical. This is because setup
is critical when the receiver is far removed from the driver. In such cases, the signal will be held
at the receiver for a long time after the clock, since the change needs a long time to propagate
from the driver to the receiver.
The recommended procedure for the I/O buffer designer to extract T
SU
is outlined below. If one
employs additional steps, it would be beneficial that any such extra steps be documented with
the results of this receiver characterization:
•
The full receiver circuit must be used, comprising the input differential amplifier, any
shaping logic gates, and the edge-triggered (or pulse-triggered) flip-flop. The output of the
flip-flop must be monitored.
•
The receiver’s Lo-to-Hi setup time should be determined using a nominal input waveform
like the one shown in Figure 12-13 (solid line). The Lo-to-Hi input starts at V
IN_LOW_MAX
(V
REF
- 200 mV) and goes to V
IN_HIGH_MIN
= V
REF
+200 mV, at a slow edge rate of
0.3V/ns, with the process, temperature, voltage, and V
REF_INTERNAL
of the receiver set to
the worst (longest T
SU
) corner values. Here, V
REF
is the external (system) reference
voltage at the device pin. Due to tolerance in V
TT
(1.5V, ±10%) and the voltage divider
generating system V
REF
from V
TT
(±2%), V
REF
can shift around 1 V by a maximum of
±122 mV. When determining setup time, the internal reference voltage V
REF_INTERNAL
(at
the reference gate of the diff. amp.) must be set to the value which yields the longest setup
time. Here, V
REF_INTERNAL
= V
REF
±(122 mV +V
NOISE
). Where, V
NOISE
is the net
maximum differential noise amplitude on the component’s internal V
REF
distribution bus
(at the amplifier’s reference input gate) comprising noise picked up by the connection from
the V
REF
package pin to the input of the amp.
•
Analogously, for the setup time of Hi-to-Lo transitions (Figure 12-14), the input starts at
V
IN_HIGH_MIN
= V
REF
+200 mV and drops to V
IN_LOW_MAX
= V
REF
- 200 mV at the rate
of 0.3V/ns.
•
For both the 0.3V/ns edge rate and faster edge rates (up to 0.8V/ns for Lo-to-Hi, and 3V/ns
for Hi-to-Lo —dashed lines in Figure 12-13 and Figure 12-14), one must ensure that lower
starting voltages of the input swing (V
START
in the range ‘V
REF
-200 mV’ to 0.5 V for Lo-
to-Hi transitions, and 1.5 V to ‘V
REF
+200 mV’ for Hi-to-Lo transitions —dashed lines in
Figure 12-13 and Figure 12-14) do not require T
SU
to be made longer. This step is needed
since a lower starting voltage may cause the input differential amplifier to require more
time to switch, due to having been in deeper saturation in the initial state.
Summary of Contents for Pentium Pro Family
Page 17: ...1 Component Introduction ...
Page 26: ...2 Pentium Pro Processor Architecture Overview ...
Page 27: ......
Page 36: ...3 Bus Overview ...
Page 62: ...4 Bus Protocol ...
Page 105: ...5 Bus Transactions and Operations ...
Page 126: ...6 Range Registers ...
Page 131: ...7 Cache Protocol ...
Page 135: ...8 Data Integrity ...
Page 148: ...9 Configuration ...
Page 161: ...10 Pentium Pro Processor Test Access Port TAP ...
Page 172: ...11 Electrical Specifications ...
Page 201: ...12 GTL Interface Specification ...
Page 229: ...13 3 3V Tolerant Signal Quality Specifications ...
Page 233: ...14 Thermal Specifications ...
Page 239: ...15 Mechanical Specifications ...
Page 241: ...15 2 MECHANICAL SPECIFICATIONS s Figure 15 1 Package Dimensions Bottom View ...
Page 252: ...16 Tools ...
Page 260: ...16 8 TOOLS Figure 16 4 Generic MP System Layout for Debug Port Connection ...
Page 264: ...17 OverDrive Processor Socket Specification ...
Page 290: ...A Signals Reference ...
Page 320: ...Index ...
Page 328: ......