Manual

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1 of 23 110901

FEATURES

§ Real-time clock (RTC)

− Counts seconds, minutes, hours, date,

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

§ 1.25V threshold detector for power-fail

warning

§ 10-bit analog-to-digital converter (ADC)

− Monotonic with no missing codes

§ Four-wire analog resistive touch-screen

interface

PIN ASSIGNMENT

ORDERING INFORMATION

DS1680FP-3 3.3V Operation

DS1680FP-5 5.0V Operation

DESCRIPTION

The DS1680 incorporates many functions necessary for low-power portable products, providing an RTC,

NV RAM controller, microprocessor monitor, power-fail warning, 10-bit ADC, and a touch-screen

controller in one chip.

The RTC provides seconds, minutes, hours, day, date, month, and year information with leap-year

compensation as well as an alarm interrupt. This interrupt works when the DS1680 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.

DS1680

Portable System Controller

with Touch-Screen Control

www.maxi

ic.com

Pin MQFP (10 x 10 x 2mm)

PFI

GND

CEI

NEW_DATA

PFO

BAT

INT

2311

CCO

RST

CEO

I/O

SCLK

OSCIN

PEN_OFF

X+

Y-

REF

AVS

Y+

AVD

AIN1

AIN0

X-

PD_RESET

PEN_SELECT

ANSELIN

CONVERT

OUT_SELECT

COEN

BHE

AVG

Package dimension information can be found at:

http://www.maxim-ic.com/TechSupport/DallasPackInfo.htm

Summary of content (23 pages)

PAGE 1
DS1680 Portable System Controller with Touch-Screen Control www.maxim-ic.
PAGE 2
DS1680 Automatic backup and write protection of an external SRAM is provided through the VCCO and CEO pins. The backup energy source used to power the RTC is also used to retain RAM data in the absence of VCC through the VCCO pin. The chip-enable output to SRAM, CE0 , is controlled during power transients to prevent data corruption. The DS1680’s microprocessor- monitor circuitry provides three basic functions.
PAGE 3
DS1680 SIGNAL DESCRIPTIONS VCC , GND (Digital Supply and Digital Ground) – DC power to the RTC, watchdog, X and Y drivers, and power-switching circuitry is provided to the device on these pins. VBAT (Backup Power Supply) – Battery input for standard 3V lithium cell or other energy source. SCLK (Serial Clock Input) – SCLK is used to synchronize data movement on the serial interface. I/O (Data Input/Output) – The I/O pin is the bidirectional data pin for the 3-wire interface.
PAGE 4
DS1680 AVD, AVS (ADC Supply and Ground) – Power supply and ground for the ADC. AIN0, AIN1 (Analog Inputs) – These pins are the analog inputs for the ADC. VREF (Voltage Reference) – Reference voltage for the ADC. X+, X- (Resistive Tablet X Plane Driver) – Connect to X-terminal of resistive tablet. Y+, Y- (Resistive Tablet Y Plane Driver) – Connect to Y-terminal of resistive tablet. CONVERT – Assert to logic 1 to request sample from AIN0 or AIN1. Use with ANSELIN input.
PAGE 5
DS1680 3-WIRE SERIAL INTERFACE Communication with the RTC and watchdog is accomplished through a simple 3-wire interface consisting of the chip select (CS), serial clock (SCLK), and input/output (I/O) pins. All data transfers are initiated by driving the CS input high. The CS input serves two functions. First, CS turns on the control logic, which allows access to the shift register for the address/command sequence.
PAGE 6
DS1680 ADDRESS/COMMAND BYTE Figure 4 shows the command byte for the DS1680. Each data transfer is initiated by a command byte. Bits 0–6 specify the address 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 zero and a write operation is selected if bit 7 is a one. The address map for the DS1680 is shown in Figure 5.
PAGE 7
DS1680 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 zero. These bits will always read zero regardless of how they are written. Also note that registers 0Eh to 7Fh are reserved. These registers will always read zero regardless of how they are written. The contents of the time, calendar, and alarm registers are in the binary-coded decimal (BCD) format.
PAGE 8
DS1680 AIE (Alarm Interrupt Enable) – When set to a logic 1, this bit permits the interrupt request flag (IRQF) bit in the status register to assert INT. When the AIE bit is set to logic 0, the IRQF bit does not initiate the INT signal. STATUS REGISTER – 0Ch BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 0 LOBAT 0 0 0 0 0 IRQF LOBAT (Low Battery Flag) – This bit reflects the status of the backup power source connected to the VBAT pin. When VBAT is greater than 2.
PAGE 9
DS1680 POWER-FAIL COMPARATOR Figure 6 +5V VCC R1 VIN PFI C1 R2 DS1680 R3 PFO GND to µP R2||R3 R1 + R2 VTRIP = 1.25 VH= 1.25 / R2 VI – 1.25 R1 1.25 5 - 1.
PAGE 10
DS1680 MICROPROCESSOR MONITOR The DS1680 monitors three vital conditions for a microprocessor: power supply, software execution, and external override. First, a precision temperature-compensated reference and comparator circuit monitors the status of VCC. When an out-of-tolerance condition occurs, an internal power-fail signal is generated that forces the RST pin to the active state, thus warning a processor-based system of impending power failure.
PAGE 11
DS1680 RESISTIVE TOUCH SCREEN (4-WIRE) Resistive touch screens consist of two resistive plates that are separated by a small gap. Each plate has an electrode at each end; when the screen is touched the pressure forces the two plates to come in contact at the exact position of the touch. To get the x-coordinate position, the DS1680 will drive the X-plane resistive film (via X+ and X-) and sense the voltage picked up by the Y-plane resistive film (via Y+ and Y-).
PAGE 12
DS1680 PROGRAMMABLE DUTY CYCLE The current required to take an X or Y measurement is VAVD / RD. In the case of RD = 250O and VAVD = 5V, the current required is 20mA. The average current is the current during the measurement, multiplied by the ratio of the time the drivers are on, to the power of total sample time. In order to minimize the average current, the on-time should be limited to the minimum time required for the tablet RC delay.
PAGE 13
DS1680 CONVERSION TIMING Figure 7a Pen Down X-Y Measure PD X Y A0 - A1 Measure PD A0 A1 PD X Y PD A0 A1 PD X Y PD A0 A1 PD X Y PD PEN_OFF AVG = 0 (Disabled) NEW_DATA AVG = 1 (Enabled) NEW_DATA X to Y MEASUREMENT Figure 7b 115 state cycles 30 PD 10-18 13-5 28-36 13-5 11 1001 00 111001 00 X-drivers on Y-drivers on 21 30 PD 1 State Cycle = 16 Main Clock Cycles AIN0 to AIN1 MEASUREMENT Figure 7c 115 state cycles 30 18 6 PD A0 35 6 20 A1 30 PD 1 State Cycle = 16 Main
PAGE 14
DS1680 CONVERT AND ANSELIN TIMING Figure 8 must be at least 2 state cycles CONVERT AIN0 conversion requested ANSELIN = 0 must be at least 4 state cycles CONVERT both AIN0 and AIN1 conversion requested ANSELIN must be at least 2 state cycles must be at least 2 state cycles must be at least 2 state cycles CONVERT AIN1 conversion requested ANSELIN = 1 14 of 23
PAGE 15
DS1680 PARALLEL INTERFACE The ADC output is available on the data bus at pins D0–D7. A logic 0 on COEN will enable data onto the data bus so that the DS1680 can be used in parallel with other devices. PEN_SELECT and OUT_SELECT are used to decode which analog output (X-, Y-, AIN0, or AIN1) is output on the data bus when COEN is asserted low. Since the device offers 10-bit resolution, the BHE pin is used to decode the 10 bits of data on the data bus. A logic 1 on BHE will enable data bits B2–B9.
PAGE 16
DS1680 ABSOLUTE MAXIMUM RATINGS* Voltage Range on Any Pin Relative to Ground Operating Temperature Range Storage Temperature Range Soldering Temperature Range -0.3V to +7.0V 0°C to +70°C -55°C to +125°C See J-STD-020A Specification *This is a stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the operation sections of this specification is not implied.
PAGE 17
DS1680 (0°C to +70°C; V CC = 3.3V ± 10%) DC ELECTRICAL CHARACTERISTICS PARAMETER Input Leakage CS Leakage Logic 1 Output (IOUT = -0.4mA) Logic 0 Output (IOUT = 1.
PAGE 18
DS1680 (0°C to +70°C; V CC = 3.3V ± 10%) 3-WIRE INTERFACE CHARACTERISTICS PARAMETER Data to Clock Setup CLK to Data Hold CLK to Data Delay CLK to Low Time CLK to High Time CLK Frequency CLK Rise and Fall CS to CLK Setup CLK to CS Hold CS Inactive Time CS to I/O High- Z SYMBOL tDC tCDH tCDD tCL tCH tCLK tR, tF tCC tCCH tCWH tCDZ Resistance of On-Chip Driver Parasitic Capacitance Between Xand Y-Plates of Digitizer Ladder Resistance TYP MAX 600 750 750 0.
PAGE 19
DS1680 (0°C to +70°C; VCC, VAVD = 3.
PAGE 20
DS1680 POWER-FAIL AND RESET CHARACTERISTICS (0ºC to +70ºC; V CC = 3.
PAGE 21
DS1680 3-WIRE TIMING DIAGRAM: READ DATA Figure 10 3-WIRE TIMING DIAGRAM: WRITE DATA Figure 11 PUSHBUTTON RESET Figure 12 21 of 23
PAGE 22
DS1680 VCC POWER-UP Figure 13 VCC POWER-DOWN Figure 14 POWER-FAIL WARNING Figure 15 22 of 23
PAGE 23
DS1680 NOTES: 1. Logic 1 voltages are specified at VCC = 3.3V or 5.0V, VOH = VCC for capacitive loads. Exclude RST pin. 2. Logic 0 voltages are specified at VCC = 3.3 or 5.0V, VOL = GND for capacitive loads. 3. ICCA is specified with outputs open, CS set to a logic 1, SCLK = 500kHz, oscillator enabled, ADC disabled, and no pen detected. 4. ICCS is specified with CS, VCCO open and I/O, SCLK at logic 0, ADC disabled, and no pen detected. 5. IAVDA is specified with ADC enabled. 6.