DS87C530_1 Datasheet, PDF (22/44 Pages) Dallas Semiconductor – EPROM/ROM Micro with Real Time Clock

DS87C530/DS83C530
The ring oscillator runs at approximately 2-4 MHz but will not be a precise value. Do not conduct real-
time precision operations (including serial communication) during this ring period. Figure 4 shows how
the operation would compare when using the ring, and when starting up normally. The default state is to
exit Stop mode without using the ring oscillator.
The RGSL - Ring Select bit at EXIF.1 (EXIF; 91h) controls this function. When RGSL = 1, the CPU will
use the ring oscillator to exit Stop mode quickly. As mentioned above, the processor will automatically
switch from the ring to the crystal after a delay of 65,536 crystal clocks. For a 3.57 MHz crystal, this is
approximately 18 ms. The processor sets a flag called RGMD- Ring Mode, located at EXIF.2, that tells
software that the ring is being used. The bit will be a logic 1 when the ring is in use. Attempt no serial
communication or precision timing while this bit is set, since the operating frequency is not precise.
RING OSCILLATOR EXIT FROM STOP MODE Figure 4
Note: Diagram assumes that the operation following Stop requires less than 18 ms to complete.
EMI REDUCTION
One of the major contributors to radiated noise in an 8051 based system is the toggling of ALE. The
DS87C530/DS83C530 allows software to disable ALE when not used by setting the ALEOFF (PMR.2)
bit to a 1. When ALEOFF = 1, ALE will still toggle during an off-chip MOVX. However, ALE will
remain in a static when performing on-chip memory access. The default state of ALEOFF = 0 so ALE
toggles with every instruction cycle.
PERIPHERAL OVERVIEW
The DS87C530/DS83C530 provides several of the most commonly needed peripheral functions in
microcomputer-based systems. These new functions include a second serial port, Power-fail Reset,
Power-fail Interrupt, and a programmable Watchdog Timer. These are described below, and more details
are available in the High-Speed Microcontroller User’s Guide.
22 of 44