82C284 Datasheet, PDF (5/11 Pages) Intersil Corporation – Clock Generator and Ready Interface for 80C286 Processors

82C284
LOW to HIGH input transition voltage. As long as the slope of
the RES input voltage remains in the same direction (increas-
ing or decreasing) around the RES input transition voltage, the
RESET output will make a single transition.
V_CC
1N914
47Ω
10kΩ
82C284
11
RES
+
10µF
FIGURE 3. TYPICAL RC RES TIMING CIRCUIT
Ready Operation
The 82C284 accepts two ready sources for the system ready
signal which terminates the current bus cycle. Either a synchro-
nous (SRDY) or asynchronous ready (ARDY) source may be
used. Each ready input has an enable (SRDYEN and
ARDYEN) for selecting the type of ready source required to ter-
minate the current bus cycle. An address decoder would nor-
mally select one of the enable inputs.
READY is enabled (LOW), if either SRDY + SRDYEN = 0 or
ARDY + ARDYEN = 0 when sampled by the 82C284 READY
generation logic. READY will remain active for at least two CLK
cycles.
The READY output has an open-drain driver allowing other
ready circuits to be wired with it, as shown in Figure 4. The
READY signal of an 80C286 system requires an external
pull-up resistor. To force the READY signal inactive (HIGH)
at the start of a bus cycle, the READY output floats when
either S1 or S0 are sampled LOW at the falling edge of CLK.
Two system clock periods are allowed for the pull-up resistor
to pull the READY signal to V_lH. When RESET is active,
READY is forced active one CLK later (see Waveforms).
7
X1
10
CLK
CLK
V_CC
80C286
8 ^X2
CPU OR
C1
82C284
SUPPORT
COMPONENT
4
6
READY
18
READY
F/C V_CC
V_CC
DECOUPLING
CAPACITOR
FIGURE 4. RECOMMENDED CRYSTAL AND READY
CONDITIONS
Figure 5 illustrates the operation of SRDY and SRDYEN.
These inputs are sampled on the falling edge of CLK when
S1 and S0 are inactive and PCLK is HIGH. READY is forced
active when both SRDY and SRDYEN are sampled as LOW.
Figure 6 shows the operation of ARDY and ARDYEN These
inputs are sampled by an internal synchronizer at each fall-
ing edge of CLK. The output of the synchronizer is then sam-
pled when PCLK is HIGH. If the synchronizer resolved both
the ARDY and ARDYEN as active, the SRDY and SRDYEN
inputs are ignored. Either ARDY or ARDYEN must be HIGH
at the end of T_S, therefore, at least one wait state is required
when using the ARDY and ARDYEN inputs as a basis for
generating READY.
READY remains active until either S1 or S0 are sampled
LOW, or the ready inputs are sampled as inactive.
5