DS1221 ,Nonvolatile Controller x 4 ChipPIN DESCRIPTION VCCO VCCIA, B - Address Inputs 2 15VBAT1 VBAT2CE - Chip Enable Input 3 14 CE*RST4 1 ..
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DS1221
Nonvolatile Controller x 4 Chip
NOT RECOMMENDED FOR NEW DESIGNS, SEE DS1321 DATASHEET INSTEAD.
FEATURESConverts CMOS RAMs into nonvolatile
memoriesData is automatically protected during power loss2-to-4 decoder provides for up to 4 CMOSRAMsProvides for redundant batteriesTest battery condition on power-upFull ±10% operating rangeUnauthorized access can be prevented withoptional security feature16-pin 0.3-inch DIP saves PC board spaceOptional 16-pin SOIC surface mount packageOptional industrial temperature range of
-40°C to +85°C available
PIN DESCRIPTIONA, B- Address Inputs- Chip Enable Input
CE0 - CE3- Chip Enable OutputsVBAT1 - + Battery 1
VBAT2 - + Battery 2RST- Reset
VCCI - +5V Supply
VCCO - RAM SupplyRD- Read InpuWE- Write Input
*D/Q- Data Input/Output
PIN ASSIGNMENT*Used with optional security circuit only and must be connected to ground in all other cases.
DESCRIPTIONThe DS1221 Nonvolatile Controller x 4 Chip is a CMOS circuit which solves the application problem of
converting CMOS RAMs into nonvolatile memories. Incoming power is monitored for an out-of-
tolerance condition. When such a condition is detected, the chip enable outputs are inhibited to
accomplish write protection and the battery is switched on to supply RAMs with uninterrupted power. An
optional security code prevents unauthorized users from obtaining access to the memory space. Thenonvolatile controller/decoder circuitry uses a low-leakage CMOS process which affords precise voltage
DS1221
Nonvolatile Controller x 4 ChipVCCO
VBAT1
*RST
*RD
*WE
GND
VCCI
VBAT2
CE0
CE2
CE3
*D/Q
CE1
DS1221 16-Pin DIP (300-mil)See Mech. Drawings Section
VCCO
VBAT1
*RST
*RD
*WE
GND
VCCI
VBAT2
CE0
CE2
CE3
*D/Q
CE1
DS1221 16-Pin SOIC (300-mil)See Mech. Drawings Section
DS1221
CONTROLLER /DECODER OPERATIONThe DS1221 nonvolatile controller performs six circuit functions required to decode and battery-backup a
bank of up to four CMOS RAMs. First, a 2-to-4 decoder provides selection of one of four RAMs (see
Figure 1). Second, a switch is provided to direct power from the battery or VCCI supply, depending on
which is greater, to the VCCO pin. This switch has a voltage drop of less than 0.2V. The third function
which the nonvolatile controller provides is power-fail detection. The DS1221 constantly monitors theVCCI supply. When VCCI falls below 4.5 volts, a precision comparator detects the condition and inhibits
the RAM chip enables (CE0 through CE3). The fourth function of write protection is accomplished by
holding all chip enable outputs (CE0 through CE3) to within 0.2 volts of VCCI or battery supply. If the
Chip Enable Input (CE) is low at the time power-fail detection occurs, the chip enable outputs are kept in
their present state until CE is driven high. The delay of write protection until the current memory cycle is
completed prevents the corruption of data. Power failure detection occurs in the range of 4.5 to 4.25 volts.
During nominal supply conditions the chip enable outputs follow the logic of a 2-to-4 decoder. The fifth
function the DS1221 performs is to check battery status to warn of potential data loss. Each time that VCCI
power is restored the battery voltage is checked with a precision comparator. If the connected batteryvoltage is less than 2 volts, the second memory cycle is inhibited. Battery status can, therefore, be
determined by performing a read cycle after power-up to any location in memory, verifying that memory
location content. A subsequent write cycle can then be executed to the same memory location, altering the
data. If the next read cycle fails to verify the written data, the contents of the memories are questionable.
The sixth function of the nonvolatile controller provides for battery redundancy. In many applications,data integrity is paramount. In these applications it is often desirable to use two batteries to ensure
reliability. The DS1221 provides an internal isolation switch which provides for connection of two
batteries. During battery back-up operation the battery with the highest voltage is selected for use. If one
battery should fail, the other will automatically take over. The switch between batteries is transparent to
the user. A battery status warning will occur if both batteries are less than 2.0 volts. If only one battery isused, the second battery input must be grounded. Figure 2 illustrates the connections required for the
DS1221 in a typical application.
NONVOLATILE CONTROLLER/DECODER Figure 1H = High Level
L = Low Level
X = Irrelevant
DS1221
TYPICAL APPLICATION Figure 2
SECURITY SEQUENCE Figure 3OUTPUT LOAD Figure 4
DS1221
ABSOLUTE MAXIMUM RATINGS*Voltage on Any Pin Relative to Ground-0.3V to +7.0V
Operating Temperature0°C to 70°C
Storage Temperature-55°C to +125°C
Soldering Temperature260°C for 10 secondsShort Circuit Output Current20 mAThis is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure toabsolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS(0°C to 70°C)
DC ELECTRICAL CHARACTERISTICS(0°C to 70°C; VCC = 4.5 to 5.5V)
(0°C to 70°C; VCC < 4.25V)
DS1221
CAPACITANCE(tA = 25°C)
AC ELECTRICAL CHARACTERISTICS(0°C to 70°C; VCC = 4.5 to 5.5V)
(0°C to 70°C; VCC < 4.5V)
NOTES:1. All voltages are referenced to ground.
2. Only one battery input is required.
3. Measured with VCCO and CE0 - CE3 open.
4. ICCO1 is the maximum average load which the DS1221 can supply to the memories.
5. Measured with a load as shown in Figure 4.
6. ICCO2 is the maximum average load current which the DS1221 can supply to the memories in the
battery back-up mode.
7. Chip enable outputs CE0 - CE3 can only sustain leakage current in the battery back-up mode.
8. tCE max. must be met to ensure data integrity on power loss.
9. tAS is only required to keep the decoder outputs glitch-free. While CE is low, the outputs (CE0 - CE3)
will be defined by inputs A and B with a propagation delay of tPD from an A or B input change.
10. For applications where higher currents are required, please see the DS1259 Battery Manager Chip
data sheet.
DS1221
SECURITY OPTIONWhen activated by Dallas Semiconductor, the security option prevents unauthorized access. A sequence
of events must occur to gain access to the memories (Figure 3). First, a dummy read cycle or a 200 ns
active low reset pulse is executed to initialize the sequence. Second, a 64-bit access code must be
consecutively written to the DS1221 using the write enable signal (WE), the chip enable signal (CE), and
the data input/output signal (DQ). The code is written to the DS1221 without regard to the address.
Actual RAM locations are not written, as the security option is intercepting the data path until access isgranted. Instead, a special 64-bit write only register is written. Following the 64 write cycles, the register
is compared to a 64-bit pattern uniquely defined by the user and programmed into the DS1221 by Dallas
Semiconductor at the time of manufacture. This pattern can only be interrogated by an intelligent
controller within the DS1221 and cannot be read by the user. If a read cycle occurs before 64 write cycles
are completed, the security sequence is aborted. When a correct match for 64 bits is received, the thirdpart of the security sequence begins by reading a 64-bit read only register. This register consists of 64 bits
also defined by the user and programmed into the DS1221 by Dallas Semiconductor at the time of
manufacture. For each of the 64 read cycles, 1 bit of the user-defined read only register is driven onto the
DQ line. This phase also requires that the 64 read cycles be consecutive. The data being read from the
read only register can be used by software to determine if the DS1221 will be permitted to be used withthat particular system. After the 64th read cycle has been executed the DS1221 is unlocked and all
subsequent memory cycles will be passed through and will become actual memory accesses based upon
address inputs. If VCC falls below 4.5 volts or the reset line is driven low, the entire security sequence
must be executed again in order to access memory locations.
NOTE:Contact Dallas Semiconductor sales office for code assignments.
SECURITY OPTION
AC ELECTRICAL CHARACTERISTICS(0°C to 70°C; VCC = 5V ± 10%)
