MC68LC302 Datasheet, PDF (116/169 Pages) Motorola, Inc – Low Power Integrated Multiprotocol Processor Reference Manual

5.18 CHIP-SELECT PINS
The chip-select pins are shown in Figure 5-14.
CS0/IOUT2
CS3–CS1
Signal Description
Figure 5-14. Chip-Select Pins
CS0/IOUT2—Chip-Select 0/Interrupt Output 2
In normal operation, this pin functions as CS0. CS0 is one of the four active-low output
pins that function as chip selects for external devices or memory. It does not activate on
accesses to the internal RAM or registers (including the BAR, SCR, or CKCR registers).
When the M68000 core is disabled, this pin operates as IOUT2. IOUT2 provides the in-
terrupt request output signal from the LC302 interrupt controller to an external CPU when
the M68000 core is disabled. This signal is asserted if an internal interrupt of level 4, 6, 7
is generated.
CS3–CS1—Chip Selects 3–1
These three active-low output pins function as chip selects for external devices or mem-
ory. CS3—CS0 do not activate on accesses to the internal RAM or registers (including the
BAR SCR, or CKCR registers).
5.19 WHEN TO USE PULLUP RESISTORS
Pins that are input-only or output-only do not require external pullups. The bidirectional bus
control signals require pullups since they are three-stated by the MC68LC302 when they are
not being driven. Open-drain signals always require pullups.
Unused inputs should not be left floating. If they are input-only, they may be tied directly to
V_CC or ground, or a pullup or pulldown resistor may be used. Unused outputs may be left
unconnected. Unused I/O pins may be configured as outputs after reset and left unconnect-
ed.
If the MC68LC302 is to be held in reset for extended periods of time in an application (other
than what occurs in normal power-on reset or board test sequences) due to a special appli-
cation requirement (such as V_DD dropping below required specifications, etc.), then three-
stated signals and inputs should be pulled up or down. This decreases stress on the device
transistors and saves power.
See the RESET pin description for the condition of all pins during reset.
MOTOROLA
MC68LC302 REFERENCE MANUAL
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