W216
PRELIMINARY
3
Overview
The W216 was designed as a single-chip alternative to the
standard two-chip Intel 440BX AGPset clock solution. It pro-
vides sufficient outputs to support most single-processor, four
SDRAM DIMM designs.
Functional Description
I/O Pin Operation
Pins 2, 8, 9, 29, and 30 are dual-purpose l/O pins. Upon power-
up these pins act as logic inputs, allowing the determination of
assigned device functions. A short time after power-up, the
logic state of each pin is latched and the pins become clock
outputs. This feature reduces device pin count by combining
clock outputs with input select pins.
An external 10-k
Ω “strapping” resistor is connected between
the l/O pin and ground or VDD. Connection to ground sets a
latch to “0,” connection to VDD sets a latch to “1.” Figure 1 and
Figure 2 show two suggested methods for strapping resistor
connections.
Upon W216 power-up, the first 2 ms of operation is used for
input logic selection. During this period, the five I/O pins (2, 8,
9, 29, 30) are three-stated, allowing the output strapping resis-
tor on the l/O pins to pull the pins and their associated capac-
itive clock load to either a logic HIGH or LOW state. At the end
of the 2-ms period, the established logic “0” or “1” condition of
the l/O pin is latched. Next the output buffer is enabled, con-
verting the l/O pins into operating clock outputs. The 2-ms tim-
er starts when VDD reaches 2.0V. The input bits can only be
reset by turning VDD off and then back on again.
It should be noted that the strapping resistors have no signifi-
cant effect on clock output signal integrity. The drive imped-
ance of clock output (<40
Ω, nominal), which is minimally af-
fected by the 10-k
Ω strap to ground or V
DD. As with the series
termination resistor, the output strapping resistor should be
placed as close to the l/O pin as possible in order to keep the
interconnecting trace short. The trace from the resistor to
ground or VDD should be kept less than two inches in length
to prevent system noise coupling during input logic sampling.
When the clock outputs are enabled following the 2-ms input
period, the specified output frequency is delivered on the pin,
assuming that VDD has stabilized. If VDD has not yet reached
full value, output frequency initially may be below target but will
increase to target once VDD voltage has stabilized. In either
case, a short output clock cycle may be produced from the
CPU clock outputs when the outputs are enabled.
GND
4, 10, 23, 26,
34, 42, 48, 53
G
Ground Connections: Connect all ground pins to the common system ground plane.
Pin Definitions (continued)
Pin Name
Pin No.
Pin
Type
Pin Description
Power-on
Reset
Timer
Output Three-state
Data
Latch
Hold
QD
W216
VDD
Clock Load
R
10 k
Ω
Output
Buffer
(Load Option 1)
10 k
Ω
(Load Option 0)
Output
Low
Output Strapping Resistor
Series Termination Resistor
Figure 1. Input Logic Selection Through Resistor Load Option
Power-on
Reset
Timer
Output Three-state
Data
Latch
Hold
QD
W216
VDD
Clock Load
R
10 k
Ω
Output
Buffer
Output
Low
Output Strapping Resistor
Series Termination Resistor
Jumper Options
Figure 2. Input Logic Selection Through Jumper Option
Resistor Value R
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