Z86D990 Datasheet, PDF (67/102 Pages) Zilog, Inc. – Low-Voltage Micro controllers with ADC

Z86D990/Z86D991 OTP and Z86L99X ROM
Low-Voltage Microcontrollers with ADC
60
Low-Battery Detect Flag (LB)
When the Z86D99/Z86L99 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-read-
able flag. 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 33)
Pad is regulating the current when
P43=0 (V_pad>V_min; see page 33)
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.
Note: The LB flag will be valid after enabling the detection for 20 µS
(design estimation, not tested in production). LB does not work
at STOP mode. It must be disabled during STOP mode in order
to reduce current.
PS003807-1002
PRELIMINARY