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> ## Appendix D. Programming Cable

> This appendix provides technical information about the Rabbit 2000`TM` microprocessor when connecting the RabbitLink and a PC via a programming cable.

> The programming cable has two connectors, labeled DIAG and PROG. The programming cable connects the PC's COM port to the programming port, which is header J8, on the RabbitLink. The programming port pin assignments are shown in Figure D-1.

> Figure D-1. Programming Port Pin Assignments

> ### The PROG Connector

> The PROG connector is used to download firmware to the RabbitLink (see Section 3.2.1, "Downloading Firmware to the RabbitLink"). Using the PROG connector to plug the programming cable into the programming port results in pulling the Rabbit 2000 SMODE lines high. This causes the Rabbit to enter cold boot mode after a reset. The reset occurs when the RFU opens the serial port of the PC with the DTR line high, then changes it to low. This pulses the reset line on the RabbitLink.

> In cold boot mode the processor runs a small program contained in an internal ROM. This program receives triplets sent by the PC. It is through this mechanism that the RFU sends firmware to the RabbitLink. Please see the Rabbit 2000 Designer's Handbook for a detailed description of triplets and the cold boot mode.

> ### The DIAG Connector

> The DIAG connector is used to configure network parameters for the RabbitLink. It is also used to treat the programming port as a regular serial port; because the programming cable contains an active circuit board that converts RS-232 voltage levels used by the PC serial port to CMOS voltage levels used by the Rabbit, the DIAG connector allows the programming cable to be used as an RS-232 to CMOS level converter for serial communication.

> The /RESET line and the SMODE1 and SMODE0 pins are not present in the DIAG connector.

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