80
AT94KAL Series FPSLIC
Rev. 1138G–FPSLI–11/03
Scanning 2-wire Serial
The SCL and SDA pins are open drain, bi-directional and enabled separately. The “Enable
Output” bits (active High) in the scan chain are supported by general boundary-scan cells.
Enabling the output will drive the pin Low from a tri-state. External pull-ups on the 2-wire bus
are required to pull the pins High if the output is disabled. The “Data Out/In” and “Clock Out/In”
bits in the scan chain are observe-only cells. Figure 46 shows how each pin is connected in
the scan chain.
Figure 46.
Boundary-scan Cells for 2-wire Serial
Scanning the Clock Pins
Figure 47 shows how each oscillator with external connection is supported in the scan chain.
The Enable signal is supported with a general boundary-scan cell, while the oscillator/clock
output is attached to an observe-only cell. In addition to the main clock, the timer oscillator is
scanned in the same way. The output from the internal RC-Oscillator is not scanned, as this
oscillator does not have external connections.
Figure 47.
Boundary-scan Cells for Oscillators and Clock Options
From Previous Cell
To Next Cell
To 2-wire
Serial Logic
From 2-wire
Serial Logic
SDA or
SCL
Enable Output
(General Boundary
Scan Cell)
Data or Clock Out/In
(Observe Only Cell)
0
1
D Q
From
previous
cell
ClockDR
ShiftDR
To
next
cell
To system logic
FF1
0
1
D Q
D Q
G
0
1
From
previous
cell
ClockDR UpdateDR
ShiftDR
To
next
cell
EXTEST
From digital logic
XTAL1/TOSC1
XTAL2/TOSC2
Oscillator
ENABLE
OUTPUT