CYB-P51 Proto Board

The CYB-P51 (Rev A) Prototyping Board is designed as a two layer board (without power and ground planes). All components, except the premounted P-51, are through-hole for easy probing and replacement of parts.

[CYB-P51 Board Photo]
  • The board has an oscillator circuit and a crystal circuit pattern, so that either may be used in the test application. A 20 MHz Oscillator is provided, as shown in this photo, and it is connected to 3V at jumper W5, as required by the P-51. See the clock circuits in the user manual for support components for the Xtal circuit.
  • An External pushbutton switch can Reset just the board while in an active ISA slot. The host software must release this hard reset of the P-51 (see P-51 Code RAM in manual).
  • The base address from the ISA host is switch selectable on a DIP-switch that is accessible from outside the computer. The required IRQ is software selectable. See the P-51 user manual for switch settings.
  • On-board Voltage regulator provides 3.3 volts to the P-51 and oscillator using the computer system's 5-volt supply. The P-51 I/O pins drive 3.3 volts and are 5-volt tolerant.
  • All of the ISA-bus signals are brought to a wire-wrap pattern at the bottom of the board, and all the P-51-to-ISA/PC104 signals are also available at that pattern. Alternatively, a micro-controller host could interface to the P-51 at that same jumper.
  • The application signals of the P-51 are brought to a 40-pin wire-wrap pattern in the same configuration as a standard 8051 DIP (with optional IDC pattern). All 8051 signals except X1, X2, Reset, EA, and PSEN are available at the 8051 pattern. Note that a row of GND posts (indicated by white circles) runs along the end of the pattern.
  • Of the excluded 8051 signals, X1 and X2 are available at the Xtal circuit, Reset is replaced by ResetDrv from the ISA-bus, and EA and PSEN are not implemented in the P-51.
  • The remaining P-51 signals (CE_out, Clk_Out, CE, and ALI) are available near the wire wrap area on W6.
  • Two input pins should be configured on W6: CE should be tied low and ALI should be pulled high.
  • Pin 40 of the 8051 socket (J3) is not connected to power. Jumper W8 allows you to connect that pin to 3 or 5 volts, or leave it open; and an LED indicates whether power appears on that pin.
  • As a convenience to your application, eight LEDs, buffered through a 74HCT244, are attached to the eight signals of the P-51 port 1 (P1.0 - P1.7).
  • Two RJ-45 jack patterns allow sixteen signals to be brought outside the system chassis. These are provided but are not mounted on the board. Alternatively, a 3x3 wire-wrap grid is also available at each location.
  • A set of power connector patterns allow the board to be used outside an ISA environment, as when using another micro-controller as a host.
  • A power indicator LED is connected to 5v.
Noise issues and considerations:

As a matter of good design practice, the signals from the P-51 should not be driven off-board without buffering, and should be protected from noisy circuitry. Your low-noise digital circuitry should be added to the on-board wire-wrap area, rather than cabling to a neighboring board. Noisy circuitry should be separated and buffered from the 3-volt area. Your production design should include a ground plane with a good grounding connection to all eight P-51 ground pins. An ISA-bus Extender is not recommended since it may introduce noise.


[CYB-P51 Circuit]