Specifications

56 Élan™SC310 Microcontroller Data Sheet
PRELIMINARY
Local Bus or Maximum ISA Bus Controller
Depending on the configuration chosen, the
ÉlanSC310 microcontroller’s pin functionality will differ.
The two different options are Local Bus and Maximum
ISA Bus modes. The pin options are selected upon
power-up reset. (See “Alternate Pin Functions” on
page 59.) Only Local Bus or Maximum ISA Bus mode
is available in a particular design. Local bus mode
does, however, provide a subset of the ISA bus. For
more information, see “Maximum ISA Interface versus
Local Bus Interface” on page 60.
Local Bus Option
The local bus interface is integrated with the memory
controller and the ISA bus controller, and it permits fast
transfers to and from external local bus peripherals,
such as video controllers. The local bus option is basi-
cally an Am386SXLV microprocessor local bus with an
LDEV
, LRDY, and CPUCLK added. Additional local bus
signals are available in this mode and are described in
“Local Bus Interface” on page 35.
Maximum ISA Bus Option
The Maximum ISA option provides the most ISA bus
signals of either of the ÉlanSC310 microcontroller bus
options. Since master cycles and ISA refresh are not
necessary in handheld designs, the ÉlanSC310 micro-
controller does not provide these signals in either bus
mode. The SYSCLK output from the ÉlanSC310 micro-
controller is a clock that is normally only used for the
external keyboard controller if one exists. This clock is
9.2 MHz and can be stopped completely.
This clock is not related to any of the ISA bus cycle tim-
ings. The ISA bus cycle timings vary depending on the
clock speed selected for the internal ISA bus clock.
Internal Resistors
The ÉlanSC300 microcontroller’s internal pull-down
and pull-up resistors are approximately 100-KΩ ± 50%
tolerance. They don’t provide the level of termination
that may be necessary to meet design noise margins or
the timing and termination requirements for different
bus specifications (e.g., ISA bus or local bus).
The internal pull-up and pull-down resistors only pro-
vide adequate termination for when the input is floating
and is in a very low noise environment, or for systems
where power consumption is too critical to allow for the
additional current associated with stronger pullups. Be-
cause of this, it is recommended that the designer use
the external pull-up and pull-down resistors (shown in
Table 25) on signals with critical timing or noise immu-
nity requirements. The external pull-up and pull-down
resistors are also recommended for additional design
margin, provided that space and power consumption
are not major issues.
Table 25. External Resistor Requirements
Signal Name Pin No.
Local Bus Maximum ISA
Notes
Pull Up
Pull
Down
Pull Up
Pull
Down
PIRQ0(IRQ3)
194 10K 10K
PIRQ1(IRQ6)
193 10K 10K
IRQ1
195 10K 10K
IOCHRDY
192 1K 1K
IOCS16
196 1K 1K
MCS16
197 1K 1K
IRQ14
198 10K 10K
DTR/CFG1
92 10K 100K 1
RTS/CFG0
93 100K 10K 1
IORESET
140 10K 10K
IRQ15
182 10K 10K
IRQ4
173 10K 10K
IOCHCHK
177 1K 1K
PULLUP
183 100K 100K