THE MAGAZINE FOR COMPUTER APPLICATIONS
Circuit Cellar Online offers articles illustrating creative solutions
and unique applications through complete projects, practical
tutorials, and useful design techniques.

THE ETHERNET DEVELOPMENT BOARD

Part 2: The Software and Firmware Exposed
by Fred Eady

Start ý The Basics ý Registers ý Bus Interface Registers ý Status and Control Registers ý InitChip ý Initiate Transmit Registers ý Address Filter Registers ý Receive and Transmit Frame Locations ý CS8900A-CQ Transmit and Receive Operations ý The Next Read ý Broadcast ý ARP ý No Cheating ý Tiger Woodsý Putter ý Whatýs the Point? ý And It Programs, Too! ý Sources and PDF

BUS INTERFACE REGISTERS

The bus interface registers are primarily used for interfacing the CS8900A-CQ to a real ISA bus. Because there is no place for an ISA connector on the PIC or the Ethernet development board, not much of the bus interface registerýs functionality is used. The ppageBaseIO, which is part of the bus interface register group, defaults to 0x300, which is the Ethernet development boardýs selected I/O base address. So, you donýt have to set it with code (good thing). You could use the ppagePID register to determine which level of CS8900A-CQ is glued to your printed circuit board, but that is just a waste of code, memory space, and CPU cycles for this application.

CS8900A-CQ 8-bit mode does not allow the use of CS8900A-CQ interrupts, EEPROM, or DMA. So, you must poll the CS8900A-CQ INTRQX line to sense transmit, receive, or error activity. For the polling to be realized, you must set up one of the INTRQX lines to transmit activity status to the PIC16F877ýs input pin. The application will use the INTRQ0 line, which is defined in the ppageINT register using the mask for INTRQ0 (0x00), as shown in Listing 5. After the interrupt is defined and enabled, you can turn on the CS8900A-CQ transmitter and receiver.

PREVIOUS • NEXT