DS12C887 IC – Real Time Clock (RTC) IC

The real-time clocks (RTCs) DS12885, DS12887, and DS12C887 are intended to be straight replacements for the DS1285 and DS1287. The devices have a real-time clock/calendar, one time-of-day alarm, three maskable interrupts with a shared interrupt output, a programmable square wave, and 114 bytes of battery-backed static RAM (113 bytes in the DS12C887 and DS12C887A). In a 24-pin enclosed DIP device, the DS12887 incorporates a quartz crystal and a lithium energy supply. At address 32h, the DS12C887 adds a century byte. For all devices, the end-of-month date is automatically modified for months with fewer than 31 days, including leap years. The devices can also be set to operate in 24-hour or 12-hour mode and have an AM/PM indicator. The status of VCC is monitored using a precision temperature-compensated circuit. If the primary power supply fails, the device immediately switches to a backup supply. When primary power is not available, a lithium coin-cell battery can be attached to the DS12885's VBAT input pin to keep the time and date running. The device is addressed via a multiplexed byte-wide interface that supports both Intel and Motorola modes of operation.

The DS1225AB and DS1225AD are 65,536-bit nonvolatile SRAMs that are structured as 8192 words by 8 bits. Each NV SRAM contains its own lithium energy source as well as control circuitry that constantly monitors VCC for out-of-tolerance conditions. When this occurs, the lithium energy source is automatically activated, and write protection is enabled permanently to avoid data corruption. The NV SRAMs can be used in place of conventional 8k ? 8 SRAMs that are directly compatible with the common byte wide 28-pin DIP standard. The devices also have the same pinout as the 2764 EPROM and 2864 EEPROM, allowing for direct replacement while improving performance. The amount of write cycles that can be performed is not limited, and no extra assistance circuitry is required for microprocessor connection.

The DS1225AB and DS1225AD are 65,536-bit nonvolatile SRAMs that are structured as 8192 words by 8 bits. Each NV SRAM contains its own lithium energy source as well as control circuitry that constantly monitors VCC for out-of-tolerance conditions. When this occurs, the lithium energy source is automatically activated, and write protection is enabled unconditionally to avoid data corruption. The NV SRAMs can be used in place of existing 8k ? 8 SRAMs that are directly compatible with the common bytewide 28-pin DIP standard. The devices also have the same pinout as the 2764 EPROM and 2864 EEPROM, allowing for straightforward replacement while improving performance. The number of write cycles that can be performed is not limited, and no additional support circuitry is required for microprocessor connection.

The NE555 IC devices are precision timing circuits capable of producing accurate time delays or oscillation. In the time delay or monostable mode of operation, the timed interval is controlled by a single external resistor and capacitor network. In the a stable mode of operation, the frequency and duty cycle can be controlled independently with two external resistors and a single external capacitor. The threshold and trigger levels normally are two-thirds and one-third, respectively, of VCC. These levels can be altered by use of the control-voltage terminal. When the trigger input falls below the trigger level, the flip-flop is set, and the output goes high. If the trigger input is above the trigger level and the threshold input is above the threshold level, the flip-flop is reset and the output is low. The reset (RESET) input can override all other inputs and can be used to initiate a new timing cycle. When RESET goes low, the flip-flop is reset, and the output goes low. When the output is low, a low impedance path is provided between discharge (DISCH) and ground. The output circuit is capable of sinking or sourcing current up to 200 mA. Operation is specified for supplies of 5V to 15V. With a 5-V supply, output levels are compatible with TTL inputs.