Z86D990 Datasheet, PDF (40/102 Pages) Zilog, Inc. – Low-Voltage Micro controllers with ADC

Z86D990/Z86D991 OTP and Z86L99X ROM
Low-Voltage Microcontrollers with ADC
33
Controlled Current Output
P43 is an open-drain output-only pin on the Z86D990/D991, but it can be config-
ured as output or Tristate High Impedance on the Z86L990/L991. To function
properly, Bit 3 of P4M must be set to zero to configure the pin as an open-drain
output. For the Z86L990/L991 after reset, P43 defaults to Tristate High Impedance
while the Z86D990/D991 P43 is always configured as output. The data at Port 4
must be initialized as it is undefined at power-on reset.
The current output is a controlled current source that is controlled by the output of
the value of P43 (see Table 9). P43 cannot be configured as input, and if P43 is
read, P43 always returns the state of the output value (1 for no sink and 0 for
sink).
P43 uses internal current reference and will draw current if it outputs a low logic
even without external connection. This applies to both Run mode and Stop mode.
Table 9. Current Sink Pad P43 Specifications (Preliminary)
Parameter
Rise time
Fall time
V_outmin
Comparator response
Regulated current
Internal resistance
Min
80 mA
Max
0.4 µ
0.02 µ
0.54 V
0.2 µ
120 mA
80 Ω
Conditions
LED load
LED load
@27C
The pad driver can function in two modes:
• controlled current output, when the voltage on the pad is over a minimum
value
V_pad > V_outmin
• resistive pull down when the driver cannot regulate the current; in this mode,
the gate of the NMOS pull down is raised to the power rail.
The I-V characteristics of the pad are presented in Figure 17.
PS003807-1002
PRELIMINARY