
12-1
CHAPTER 12
GTL+ INTERFACE SPECIFICATION
This section defines the new open-drain bus called GTL+. The primary target audience is de-
signers developing systems using GTL+ devices such as the Pentium Pro processor and the
82450 PCIset. This specification will also be useful for I/O buffer designers developing an I/O
cell and package to be used on a GTL+ bus.
This specification is an enhancement to the GTL (Gunning Transceiver Logic) specification.
The enhancements were made to allow the interconnect of up to eight devices operating at 66.6
MHz and higher using manufacturing techniques that are standard in the microprocessor indus-
try. The specification enhancements over standard GTL provide better noise margins and re-
duced ringing. Since this specification is different from the GTL specification, it is referred to
as GTL+.
The GTL+ specification defines an open-drain bus with external pull-up resistors providing ter-
mination to a termination voltage (V
TT
). The specification includes a maximum driver output
low voltage (V
OL
) value, output driver edge rate requirements, example AC timings, maximum
bus agent loading (capacitance and package stub length), and a receiver threshold (V
REF
) that is
proportional to the termination voltage.
The specification is given in two parts. The first, is the system specification which describes the
system environment. The second, is the actual I/O specification, which describes the AC and DC
characteristics for an I/O transceiver.
Note that some of the critical distances, such as routing length, are given in electrical length
(time) instead of physical length (distance). This is because the system design is dependent on
the propagation time of the signal on a printed circuit board trace rather than just the length of
the trace. Different PCB materials, package materials and system construction result in different
signal propagation velocities. Therefore a given physical length does not correspond to a fixed
electrical length. The distance (time) calculation up to the designer.
12.1.
SYSTEM SPECIFICATION
Figure 12-1 shows a typical system that a GTL+ device would be placed into. The typical system
is shown with two terminations and multiple transceiver agents connected to the bus. The re-
ceivers have differential inputs connected to a reference voltage, V
REF
, which is generated ex-
ternally by a voltage divider. Typically, one voltage divider exists at each component. Here one
is shown for the entire network.
Содержание Pentium Pro Family
Страница 17: ...1 Component Introduction ...
Страница 26: ...2 Pentium Pro Processor Architecture Overview ...
Страница 27: ......
Страница 36: ...3 Bus Overview ...
Страница 62: ...4 Bus Protocol ...
Страница 105: ...5 Bus Transactions and Operations ...
Страница 126: ...6 Range Registers ...
Страница 131: ...7 Cache Protocol ...
Страница 135: ...8 Data Integrity ...
Страница 148: ...9 Configuration ...
Страница 161: ...10 Pentium Pro Processor Test Access Port TAP ...
Страница 172: ...11 Electrical Specifications ...
Страница 201: ...12 GTL Interface Specification ...
Страница 229: ...13 3 3V Tolerant Signal Quality Specifications ...
Страница 233: ...14 Thermal Specifications ...
Страница 239: ...15 Mechanical Specifications ...
Страница 241: ...15 2 MECHANICAL SPECIFICATIONS s Figure 15 1 Package Dimensions Bottom View ...
Страница 252: ...16 Tools ...
Страница 260: ...16 8 TOOLS Figure 16 4 Generic MP System Layout for Debug Port Connection ...
Страница 264: ...17 OverDrive Processor Socket Specification ...
Страница 290: ...A Signals Reference ...
Страница 320: ...Index ...
Страница 328: ......