Getting Connected To The Internet Can Earn You Cash.
| Attention
Creative Design Engineers: Getting Connected To The Internet Can Earn You Cash. |
|
|
Internet Connectivity Category Winners First Prize Second Prize Third Prize Internet Application Category Winners First Prize Second Prize Third Prize
|
INTERNET PIC 2000 CONTEST WINNERS MAKING THE CONNECTION SECOND
PRIZE WINNER Lindsay Meek This design is a low-cost solution to broadcasting small packets of digitized data over a 10Base-T Ethernet network. The core chipset consists of a 20-MHz PIC16C71, an IDT 7201 512 x 8 FIFO, and a 22V10 PLD. The PIC is responsible for performing data acquisition, packet framing and assembly, CRC32 generation, as well as controlling the PLD and FIFO devices. Each Ethernet packet is assembled inside the FIFO memory by the PIC, and then shifted out onto the physical interface at the required 20 Mbps by a state machine within the PLD. The primary use of this system would be as a low-cost, high-bandwidth telemetry solution for LANs using Internet technology. The PIC uses a sampling interrupt to acquire data from its internal 8-bit ADC. This interrupt stores the samples in a circular buffer, which are then picked up by a background process and encoded into an UDP/IP Ethernet packet. This packet is stored directly into the FIFO by encoding it one nibble at a time. When the PIC has determined that the FIFO is full, the data transmission to the Ethernet network is initiated by asserting the /START control line, which activates a state machine within the PLD. During the transmission of a packet, the PLD requests nibbles of data from the FIFO by asserting the /RD signal. Each nibble is latched into an internal register, where it is combined serially with a 20-MHz clock using the Manchester encoding scheme. This is a bipolar edge-based technique that encodes a digital "1" as +1/-1 and a digital "0" as -1/+1. The TX+ and TX- outputs are fed to an isolating pulse transformer, which couples to the Ethernet network. Manchester encoding has the additional benefit of eliminating DC offset problems in the transformer. The transmission continues until the FIFO is emptied of its data, as indicated by the /EMPTY line. In order to simplify the design and configuration of the system, the destination network address is hard-coded to be a private subnet address 192.168.1.255 (netmask 255.255.0.0) . The source MAC and IP address is uniquely specified for each PIC by a ROM constant. This allows the source of packet to be identified in the case where there are multiple units on a network.
|
|
 |
 |
 |
