Z86E3016PSG Datasheet, PDF (130/348 Pages) Zilog, Inc. – Z86E3016PSG

Z8 Family of Microcontrollers
User Manual
112
ing, the state of the autolatch will be at either supply, but which state is
unpredictable.
There are four operating conditions which will activate the autolatches.
The first, which occurs when the input pin is physically disconnected
from any source, is the most obvious. The second occurs when the input is
connected to the output of a device with tri-state capability.
The autolatch will also activate when the input voltage at the pin is not
within 200 microvolts or so of either supply rail. In this case, the circuit
will draw current, which is not significant compared to the I_CC operating
current of the device, but will increase I_CC2 STOP mode current of the
device dramatically.
The fourth condition occurs when the I/O bit is configured as an output.
Referring to the output section of Figure 65, there are two ways of tri-stat-
ing the port pin. The first is by configuring the port as an input, which dis-
ables the OE signal turning both transistors off. The second can be
achieved in output mode by writing a 1 to the output port, then activating
the open drain mode. Both transistors are again off, and the port bit is in a
high impedance state. The autolatches then pull the input section toward
V_DD.
Autolatch Model
The autolatch’s equivalent circuit is shown in Figure 66. When the input
is high, the circuit consists of a resistance Rp from V_DD (the P-channel
transistor in its ON state) and a much greater resistance Rh to G_ND. Cur-
rent I_AO flows from V_DD to the output. When the input is low, the circuit
may be modeled as a resistance Rp from G_ND (the N-channel transistor in
the ON state) and a much greater resistance Rh to V_DD. Current I_AO now
flows from the input to ground. The autolatch is characterized with
respect to I_AO, so the equivalent resistance Rp is calculated according to
R_P = (V_DD–V_IN)/I_AO. The worst case equivalent resistance Rp (min) may
be calculated at the worst case input voltage, V_I = V_IH (min).
I/O Ports
UM001602-0904