Freescale Semiconductor, Inc.
load capacitance on the chip-select (CS≈) signal is not exceeded. (Address buffers may
be needed, however.)
10.1.4 ROM Interface
Using the programmable chip selects creates a very straightforward ROM interface. As
shown in Figure 10-6, no external circuitry is needed. Care must be used, however, not to
overload the address bus. Address buffers may be required to ensure that the total system
input capacitance on the address signals does not exceed the C specification.
L
MC68340
A16–A1
16-BIT
ROM
D15–D0
CS0
CE
CE
Figure 10-6. ROM Interface
10.1.5 Serial Interface
The necessary circuitry to create an RS-232 interface with the MC68340 includes an
external crystal and an RS-232 receiver/driver (see Figure 10-7). The resistor and
capacitor values shown are typical; the crystal manufacturer's documentation should be
consulted for specific recommendations on external component values. The circuit shown
does not include modem support (ready-to-send (RTS) and clear-to-send (CTS) are not
shown); however, these signals can be connected to the receiver/driver and to the
connector in a similar manner as the connections for TxDx and RxDx.
10-4
MC68340 USER’S MANUAL
MOTOROLA
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