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4.1.1 Memory I/O Interface
The Rabbit 3000 address lines (A0–A19) and all the data lines (D0–D7) are routed
internally to the onboard flash memory and SRAM chips. I/0 write (/IOWR) and I/0 read
(/IORD) are available for interfacing to external devices.
Parallel Port A can also be used as an external I/O data bus to isolate external I/O from the
main data bus. Parallel Port B pins PB2–PB7 can also be used as an auxiliary address bus.
When using the external I/O bus, you must add the following line at the beginning of your
program.
#define PORTA_AUX_IO
4.1.2 LEDs
The RCM3209 has three Ethernet status LEDs located beside the RJ-45 Ethernet jack—
these are discussed in Section 4.2.
4.1.3 Other Inputs and Outputs
The status, /RESET_IN, SMODE0 and SMODE1 I/O are normally associated with the
programming port. Since the status pin is not used by the system once a program has been
downloaded and is running, the status pin can then be used as a general-purpose CMOS
output. The programming port is described in more detail in Section 4.2.3.
/RES is an output from the reset circuitry that can be used to reset external peripheral
devices.
4.1.4 5 V Tolerant Inputs
The RCM3209/RCM3229 operates over a voltage from 3.15 V to 3.45 V, but most
RCM3209/RCM3229 input pins, except /RESET_IN, VRAM, VBAT_EXT, and the
power-supply pins, are 5 V tolerant. When a 5 V signal is applied to 5 V tolerant pins, they
present a high impedance even if the Rabbit power is off. The 5 V tolerant feature allows 5
V devices that have a suitable switching threshold to be connected directly to the
RCM3209/RCM3229. This includes HCT family parts operated at 5 V that have an input
threshold between 0.8 and 2 V.
NOTE: CMOS devices operated at 5 V that have a threshold at 2.5 V are not suitable for
direct connection because the Rabbit 3000 outputs do not rise above VDD, and is often
specified as 3.3 V. Although a CMOS input with a 2.5 V threshold may switch at 3.3 V,
it will consume excessive current and switch slowly.
In order to translate between 5 V and 3.3 V, HCT family parts powered from 5 V can be
used, and are often the best solution. There is also the "LVT" family of parts that operate
from 2.0 V to 3.3 V, but that have 5 V tolerant inputs and are available from many suppli-
ers. True level-translating parts are available with separate 3.3 V and 5 V supply pins, but
these parts are not usually needed, and have design traps involving power sequencing.
User's Manual
// required to enable external I/O bus
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