Hayes Microcomputer Products RCV56HCF - Manual (Page 51)

RCV56HCF PCI/CardBus Modem Designer’s Guide
1129 ROCKWELL PROPRIETARY INFORMATION 4-3
10. Minimize the number of through-hole connections (feedthroughs/vias) on traces carrying high frequency signals.
11. Keep all signal traces away from crystal circuits.
12. Distribute high frequency signals continuously on a single trace rather than several traces radiating from one point.
13. Provide adequate clearance (e.g., 60 mil minimum) around feedthroughs in any internal planes in the DAA circuit.
14. Eliminate ground loops, which are unexpected current return paths to the power source.
4.1.4 Power
1. Identify digital power (VDD) and analog power (AVDD) supply connections.
2. Place a 10 µF electrolytic or tantalum capacitor in parallel with a ceramic 0.1 µF capacitor between power and ground at
one or more points in the digital section. Place one set nearest to where power enters the PCB (edge connector or
power connector) and place another set at the furthest distance from where power enters the PCB. These capacitors
help to supply current surge demands by the digital circuits and prevent those surges from generating noise on the
power lines that may affect other circuits.
3. For 2-layer boards, route a 200-mil wide power trace on two edges of the same side of the PCB around the border of
the circuits using the power. (Note that a digital ground trace should likewise be routed on the other side of the board.)
4. Generally, route all power traces before signal traces.
Table 4-1. Modem Pin Noise Characteristics
Device Function Noise Source Neutral Noise Sensitive
MDP VDD, VAA 13, 27, 40, 49, 63, 85-86
144-Pin TQFP GND, DGND, AGND 16, 39, 48, 81, 99
Crystal 87-88
Control 17, 35, 56, 68
Line Interface 31-32, 37, 47, 78 25-26, 29-30, 33-34,
36
Speaker Interface 38 28
Serial/LED Interface 7, 10-11, 64, 66, 82 9, 12, 67, 75, 77, 79
Host Interface 1-6, 89-98 80
MDP Interconnect 8, 18-24, 41-46, 50-55, 59-60, 62
Reserved or NC 14-15, 57-58, 61, 65, 69-74, 76, 83-
84, 100