Z86L972 Datasheet, PDF (62/91 Pages) Zilog, Inc. – Low-Voltage Microcontrollers

Z86L972/Z86L973/Z86L974
Low-Voltage Microcontrollers
55
Low-Battery Detect Flag (LB)
When the Z86L972/Z86L973/Z86L974 is used in a battery-operated application,
one of the on-chip comparators can be used to check that the V_CC is at the
required level for correct operation of the device. When voltage begins to
approach the V_BO point, an on-chip low-battery detection circuit is tripped, which
in turn sets a user-readable flag. The low-voltage detection level (V_LB) is set to
V_BO + 0.4 V. The LB register, as described in Table 18, is used to set and reset the
LB flag.
Table 18. LB Register (Group/Bank 0Dh, Register C)
Bit
7
6
5
4
3
2
1
0
Bit/Field Reserved
Pad LVD_ LVD_
LVD Flag Enable
R/W
W
W
W
W
W
R/W R/W R/W
Reset
1
1
1
1
1
X
0
0
R = Read, W = Write, X = Indeterminate
Bit
Position
Bit/Field
R/W Value Description
76543___ Reserved
R
1
W
X
Always reads 11111
No Effect
_____2__ Pad LVD
R
1
R
0
W
X
Pad is not regulated when P43=0
(V_pad<V_min; see page 28)
Pad is regulating the current when
P43=0 (V_pad>V_min; see page 28)
Reset Pad LB flag
______1_ LVD_Flag
R
1
R
0
W
X
LB Flag Set if V_DD<V_LV
LB Flag Reset
No Effect
_______0 LVD_Enable
R/W 1
0
Enable LB *
Disable LB
Note: * When LVD is enabled, IRQ5 is set only for low-voltage detection. Timer 1 will not generate
an interrupt request.
Interrupt Control Registers
The Z8 allows up to six different interrupts from a variety of sources. These inter-
rupts can be masked and their priorities set by using the Interrupt Mask Register
and Interrupt Priority Register. The Interrupt Request Register stores the interrupt
requests for both vectored and polled interrupts.
PS010504-1002
PRELIMINARY