DS1670
Portable System Controller
www.maxim-ic.com
GENERAL DESCRIPTION
The DS1670 portable system controller is a circuit
that incorporates many of the functions necessary for
low-power portable products integrated into one chip.
The device provides a real-time clock (RTC), NV
RAM controller, microprocessor monitor, and a
3-channel, 8-bit analog-to-digital converter (ADC).
Communication with the DS1670 is established
through a simple 3-wire interface.
The RTC provides seconds, minutes, hours, day,
date, month, and year information with leap year
compensation. The RTC also provides an alarm
interrupt. This interrupt works when the DS1670 is
powered by the system power supply or when in
battery-backup operation, so the alarm can be used to
wake up a system that is powered down.
Automatic backup and write protection of an external
SRAM is provided through the V
CCO
,
CEOL,
and
CEOH
pins. The backup energy source used to power
the RTC is also used to retain RAM data in the
absence of V
CC
through the V
CCO
pin. The chip-
enable outputs to RAM (CEOL and
CEOH)
are
controlled during power transients to prevent data
corruption.
FEATURES
Provides Real-Time Clock
Counts Seconds, Minutes, Hours, Date of the
Month, Month, Day of the Week, and Year
with Leap Year Compensation Valid Up to
2100
Power-Control Circuitry Supports System
Power-On from Day/Time Alarm
Microprocessor Monitor
Halts Microprocessor During Power Fail
Automatically Restarts Microprocessor after
Power Failure
Monitors Pushbutton for External Override
Halts and Resets an Out-of-Control
Microprocessor
NV RAM Control
Automatic Battery Backup and Write Protection
to External SRAM
3-Channel, 8-Bit ADC
Simple 3-Wire Interface
3.3V Operation
Underwriters Laboratory (UL) Recognized
PIN CONFIGURATION
TOP VIEW
V
BAT
V
CCO
1
2
3
4
5
6
7
8
9
10
DS1670
20
19
18
17
16
15
14
13
12
11
ST
V
CC
X1
X2
AIN0
AIN1
AIN2
RST
BLE
BHE
ORDERING INFORMATION
VOLTAGE
PART*
(V)
DS1670E
3.3
DS1670E+
3.3
DS1670E/T&R
3.3
DS1670E+TRL
3.3
DS1670S
3.3
DS1670S+
3.3
PIN-
PACKAGE
20 TSSOP
20 TSSOP
20 TSSOP
20 TSSOP
20 SO
20 SO
TOP MARK†
DS1670E
DS1670E
DS1670E
DS1670E
DS1670S
DS1670S
SCLK
I/O
CS
CEI
CEOL
CEOH
INT
GND
*
All devices are specified over the 0°C to +70°C operating range.
†
A “‘+” anywhere on the top mark denotes a lead-free device.
+ Denotes a lead(Pb)-free/RoHS-compliant device.
TSSOP (4.4mm)
SO (300 mils)
1 of 16
REV: 080805
DS1670
DETAILED DESCRIPTION
The microprocessor monitor circuitry of the DS1670 provides three basic functions. First, a precision
temperature-compensated reference and comparator circuit monitors the status of V
CC
. When an out-of-
tolerance condition occurs, an internal power-fail signal is generated that forces the reset to the active
state. When V
CC
returns to an in-tolerance condition, the reset signals are kept in the active state for
250ms to allow the power supply and processor to stabilize. The second microprocessor monitor function
is pushbutton reset control. The DS1670 debounces a pushbutton input and guarantees an active-reset
pulse width of 250ms. The third function is a watchdog timer. The DS1670 has an internal timer that
forces the reset signals to the active state if the strobe input is not driven low prior to watchdog timeout.
The DS1670 also provides a 3-channel, 8-bit successive approximation analog-to-digital converter. The
converter has an internal 2.55V (typical) reference voltage generated by an on-board band-gap circuit.
The ADC is monotonic (no missing codes) and has an internal analog filter to reduce high frequency
noise.
OPERATION
The block diagram in Figure 1 shows the main elements of the DS1670. The following paragraphs
describe the function of each pin.
DS1670 BLOCK DIAGRAM
Figure 1
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DS1670
PIN DESCRIPTION
PIN
1
NAME
V
BAT
FUNCTION
Battery Input for Standard 3V Lithium Cell or Other Energy Source. UL recognized to
ensure against reverse charging when used with a lithium battery. Go to
www.maxim-
ic.com/qa/info/ul/.
External SRAM Power Supply Output. This pin is internally connected to V
CC
when V
CC
is
within nominal limits. However, during power-fail V
CCO
is internally connected to the
V
BAT
pin. Switchover occurs when V
CC
drops below the lower of V
BAT
or 2.7V.
Serial Clock Input. Used to synchronize data movement on the serial interface.
Data Input/Output. This pin is the bidirectional data pin for the 3-wire interface.
Chip Select. Must be asserted high during a read or a write for communication over the 3-
wire serial interface. CS has an internal 40k pulldown resistor.
RAM Chip-Enable In. Must be driven low to enable the external RAM.
RAM Chip-Enable Out Low. Active-low chip-enable output for low-order SRAM byte.
RAM Chip-Enable Out High. Active-low chip-enable output for high-order SRAM byte.
Interrupt Output. This pin is an active-high output that can be used as an interrupt input to
a microprocessor. The INT output remains high as long as the status bit causing the
interrupt is present and the corresponding interrupt-enable bit is set. The INT pin operates
when the DS1670 is powered by V
CC
or V
BAT
.
Ground. DC power is provided to the device on this pin.
Byte High-Enable Input. This pin when driven low activates the
CEOH
output if
CEI
is
also driven low.
Byte Low-Enable Input. This pin when driven low activates the
CEOL
output if
CEI
is
also driven low.
Active-Low Reset. The
RST
pin functions as a microprocessor reset signal. This pin is
driven low 1) when V
CC
is outside of nominal limits; 2) when the watchdog timer has
timed out; 3) during the power up reset period; and 4) in response to a pushbutton reset.
The
RST
pin also functions as a pushbutton reset input. When the
RST
pin is driven low,
the signal is debounced and timed such that a
RST
signal of at least 250ms is generated.
This pin has an open-drain output with an internal 47k pullup resistor.
Analog Inputs. These pins are the three analog inputs for the 3-channel ADC.
Connections for Standard 32.768kHz Quartz Crystal. For greatest accuracy, the DS1670
must be used with a crystal that has a specified load capacitance of 6pF. There is no need
for external capacitors or resistors. Note: X1 and X2 are very high-impedance nodes. It is
recommended that they and the crystal be guard-ringed with ground and that high
frequency signals be kept away from the crystal area. For more information on crystal
selection and crystal layout considerations, refer to
Application Note 58: Crystal
Considerations with Dallas Real Time Clocks.
The DS1670 does not function without a
crystal.
+3.3V Input DC Power. When 3.3V is applied within nominal limits, the device is fully
accessible and data can be written and read. When V
CC
drops below 2.88V (typical) access
to the device is prohibited. When V
CC
drops below the lower of V
BAT
and 2.7V (typical),
the device is switched over to the backup power supply.
Active-Low Strobe Input. The strobe input pin is used with the watchdog timer. If the
ST
pin is not driven low within the watchdog time period, the
RST
pin is driven low.
2
3
4
5
6
7
8
9
10
11
12
V
CCO
SCLK
I/O
CS
CEI
CEOL
CEOH
INT
GND
BHE
BLE
13
RST
14,
15, 16
AIN2,
AIN1,
AIN0
17, 18
X2, X1
19
V
CC
ST
20
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DS1670
POWER-UP/POWER-DOWN CONSIDERATIONS
The DS1670 was designed to operate with a power supply of 3.3V. When 3.3V are applied within
nominal limits, the device becomes fully accessible after t
RPU
(250ms typical). Before t
RPU
elapses, all
inputs are disabled. When V
CC
drops below 2.88V (typical), the
RST
pin is driven low. When V
CC
drops
below the lower of 2.7V (typical) or the battery voltage, the device is switched over to the backup power
supply.
During power-up, when V
CC
returns to an in-tolerance condition, the
RST
pin is kept in the active state
for 250ms (typical) to allow the power supply and microprocessor to stabilize.
ADDRESS/COMMAND BYTE
The command byte for the DS1670 is shown in Figure 2. Each data transfer is initiated by a command
byte. Bits 0 through 6 specify the addresses of the registers to be accessed. The MSB (bit 7) is the
Read/Write bit. This bit specifies whether the accessed byte will be read or written. A read operation is
selected if bit 7 is a 0 and a write operation is selected if bit 7 is a 1. The address map for the DS1670 is
shown in Figure 3.
ADDRESS/COMMAND BYTE
Figure 2
7
RD
6
A6
5
A5
4
A4
3
A3
2
A2
1
A1
0
A0
WR
DS1670 ADDRESS MAP
Figure 3
BIT 7
00
01
02
03
04
05
06
07
08
09
0A
0B
0C
0D
0E
0F
7F
0
0
0
0
0
0
BIT 0
10 SECONDS
SECONDS
10 MINUTES
MINUTES
12
10 HR
10 HR
HOURS
24
A/P
0
0
0
0
DAY
0
10 DATE
DATE
0
0
10
MONTH
MO.
10 YEAR
YEAR
10 SEC ALARM
SECONDS ALARM
10 MIN ALARM
MINUTES ALARM
12
10 HR
10 HR
HOUR ALARM
24
A/P
0
0
0
DAY ALARM
CONTROL REGISTER
STATUS REGISTER
WATCHDOG REGISTER
ADC REGISTER
RESERVED
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M
M
M
M
DS1670
CLOCK, CALENDAR, AND ALARM
The time and calendar information is accessed by reading/writing the appropriate register bytes. Note that
some bits are set to 0. These bits will always read 0 regardless of how they are written. Also note that
registers 0 Fh to 7 Fh are reserved. These registers will always read 0 regardless of how they are written.
The contents of the time, calendar, and alarm registers are in the Binary-Coded Decimal (BCD) format.
The DS1670 can run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the
12-hour or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5
is the AM/PM bit with logic 1 being PM. In the 24-hour mode, bit 5 is the second 10-hour bit (20-23
hours).
The DS1670 also contains a time of day alarm. The alarm registers are located in registers 07h to 0 Ah.
Bit 7 of each of the alarm registers are mask bits (see Table 1). When all of the mask bits are logic 0, an
alarm will occur once per week when the values stored in timekeeping registers 00h to 03h match the
values stored in the time of day alarm registers. An alarm will be generated every day when mask bit of
the day alarm register is set to 1. An alarm will be generated every hour when the day and hour alarm
mask bits are set to 1. Similarly, an alarm will be generated every minute when the day, hour, and minute
alarm mask bits are set to 1. When day, hour, minute, and seconds alarm mask bits are set to 1, an alarm
will occur every second.
TIME OF DAY ALARM BITS
Table 1
ALARM REGISTER MASK BITS (BIT 7)
SECONDS MINUTES HOURS DAYS
1
1
1
1
0
1
1
1
0
0
1
1
0
0
0
1
0
0
0
0
DESCRIPTION
Alarm once per second.
Alarm when seconds match.
Alarm when minutes and seconds match
Alarm when hours, minutes and seconds match.
Alarm when day, hours, minutes and seconds.
SPECIAL PURPOSE REGISTERS
The DS1670 has two additional registers (control register and status register) that control the real-time
clock and interrupts.
CONTROL REGISTER
BIT 7
EOSC
EOSC
BIT 6 BIT 5
WP
AIS1
BIT 4
AIS0
BIT 3
0
BIT 2
0
BIT 1
0
BIT 0
AIE
(Enable Oscillator).
This bit when set to logic 0 will start the oscillator. When this bit is set to a
logic 1, the oscillator is stopped and the DS1670 is placed into a low-power standby mode with a current
drain of less than 200nA when in battery-backup mode. When the DS1670 is powered by V
CC
, the
oscillator is always on regardless of the status of the
EOSC
bit; however, the real-time clock is
incremented only when
EOSC
is a logic 0.
WP (Write Protect).
Before any write operation to the real time clock or any other registers, this bit
must be logic 0. When high, the write-protect bit prevents a write operation to any register.
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