RCM2000 datasheet(32/80 Pages) DIGI

32 / 80 page

RabbitCore RCM2000

4.2 Memory I/O Interface

Thirteen of the Rabbit 2000 address lines (A0–A12) and all the data lines (D0–D7) are

available as outputs on the RCM2000. I/0 write (/IOWR), I/0 read (/IORD), buffer enable

(/BUFEN), and Watchdog Output (/WDO) are also available for interfacing to external

devices.

The STATUS output has three different programmable functions:

1. It can be driven low on the first op code fetch cycle.

2. It can be driven low during an interrupt acknowledge cycle.

3. It can also serve as a general-purpose output.

4.2.1 Additional I/0

Although, the output clock is available on the PCLK pin, the output clock is disabled in

software starting with Dynamic C v 7.02 and later. This reduces radiated emissions. The

primary function of PCLK is as a peripheral clock or a peripheral clock ÷ 2, but PCLK can

instead be used as a digital output. See Section 5.2.1, “PCLK Output,” for more informa-

tion.

Two status mode pins, SMODE0 and SMODE1, are available as inputs. The logic state of

these two pins determines the startup procedure after a reset. /RES_IN is an external input

used to reset the Rabbit 2000 microprocessor and RCM2000 memory. /RES_OUT is an

output from the reset circuitry that can be used to reset other peripheral devices.

4.3 Serial Communication

The RCM2000 does not have an RS-232 or an RS-485 transceiver directly on the board.

However, the Prototyping Board does support a industry standard RS-232 transceiver

chip. See Appendix B, “Prototyping Board,” for more information.

4.3.1 Serial Ports

There are four serial ports designated as Serial Ports A, B, C, and D. All four serial ports

can operate in an asynchronous mode up to the baud rate of the system clock divided by

32. An asynchronous port can handle 7 or 8 data bits. A 9th bit address scheme, where an

additional bit is sent to mark the first byte of a message, is also supported. Serial Ports A

and B can be operated alternately in the clocked serial mode. In this mode, a clock line

synchronously clocks the data in or out. Either of the two communicating devices can sup-

ply the clock. When the Rabbit provides the clock, the baud rate can be up to 1/4 of the

system clock frequency, or more than 6.45 Mbps for a 25.8 MHz clock speed.

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