Z86L972 Datasheet, PDF (30/91 Pages) Zilog, Inc. – Low-Voltage Microcontrollers

Z86L972/Z86L973/Z86L974
Low-Voltage Microcontrollers
23
The functions and applications of these registers are explained in “Stop-Mode
Recovery Control Registers” on page 75.
Low-Voltage Standby
An on-chip voltage comparator checks that the V_CC level is at the required level
for correct operation of the Z8. When V_CC falls below the low-voltage trip voltage
(V_LV), reset is globally driven, and then the device is put in a low-current standby
mode with the external oscillator stopped. If the V_CC remains above V_RAM, the
RAM content is preserved.
When the power level rises above the V_LV level, the device performs a POR and
functions normally.
The minimum operating voltage varies with temperature and operating frequency,
while V_LV varies with temperature only.
I/O Ports
The Z86L972/Z86L973/Z86L974 family has up to 32 lines dedicated to input and
output in the 40-pin configuration. These lines are grouped into four 8-bit ports
known as Port 2, Port 4, Port 5, and Port 6. All four ports are bit programmable as
either inputs or outputs with the exception of P52, P53, and P43. P52 and P53 are
input only as they are used in factory programming. P43 is the controlled current
output and is therefore output only.
All ports have push-pull CMOS outputs. In addition, the push-pull outputs can be
turned off for open-drain operation using the P456CON register.
Internal resistive pull-up transistors are available as a user-defined mask option
on all ports. For Ports 4, 5, and 6, the pull-ups are nibble selectable. For Port 2,
the pull-up option applies to all eight I/O lines.
Note: Internal pull-ups are disabled on any given pin or group of port
pins when those pins are programmed as outputs.
Mode Registers
Each port has an associated Mode Register that determines the port’s functions
and allows dynamic change in port functions during program execution. Port and
Mode Registers are mapped into the Standard Register File. Because of their
close association, Port and Mode Registers are treated like any other
general-purpose register. There are no special instructions for port manipulation.
Any instruction that addresses a register can address the ports. Data can be
directly accessed in the Port Register, with no extra moves.
PS010504-1002
PRELIMINARY