DS87C530_1 Datasheet, PDF (11/44 Pages) Dallas Semiconductor – EPROM/ROM Micro with Real Time Clock

DS87C530/DS83C530
pin. The nominal battery voltage is 3V. The V_BAT pin will not source current. Therefore, a super cap
requires an external resistor and diode to supply charge.
The backup lifetime is a function of the battery capacity and the data retention current drain. This drain is
specified in the electrical specifications. The circuit loads the V_BAT only when V_CC has fallen below V_BAT.
Thus the actual lifetime depends not only on the current and battery capacity, but also on the portion of
time without power. A very small lithium cell provides a lifetime of more than 10 years.
INTERNAL BACKUP CIRCUIT Figure 3
IMPORTANT APPLICATION NOTE
The pins on the DS87C530/DS83C530 are generally as resilient as other CMOS circuits. They have no
unusual susceptibility to electrostatic discharge (ESD) or other electrical transients. However, no pin on
the DS87C530/DS83C530 should ever be taken to a voltage below ground. Negative voltages on any
pin can turn on internal parasitic diodes that draw current directly from the battery. If a device pin is
connected to the “outside world” where it may be handled or come in contact with electrical noise,
protection should be added to prevent the device pin from going below -0.3V. Some power supplies can
give a small undershoot on power up, which should be prevented. Application Note 93, “Design
Guidelines for Microcontrollers Incorporating NV RAM,” discusses how to protect the
DS87C530/DS83C530 against these conditions.
MEMORY RESOURCES
Like the 8051, the DS87C530/DS83C530 uses three memory areas. The total memory configuration of
the device is 16kB of ROM, 1kB of data SRAM and 256 bytes of scratchpad or direct RAM. The 1kB of
data space SRAM is read/write accessible and is memory mapped. This on-chip SRAM is reached by the
MOVX instruction. It is not used for executable memory. The scratchpad area is 256 bytes of register
mapped RAM and is identical to the RAM found on the 80C52. There is no conflict or overlap among the
256 bytes and the 1 kB as they use different addressing modes and separate instructions.
OPERATIONAL CONSIDERATION
The erasure window of the windowed CERQUAD should be covered without regard to the programmed/
unprogrammed state of the EPROM. Otherwise, the device may not meet the AC and DC parameters
listed in the datasheet.
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