Spark Logic

Intel 8051 connection guide

Intel 8051 DIP-40 wiring guide with power, signal assignments, and bench checks.

DIP-40

40 contacts Current package

Intel · Original dual-inline package shown in Intel’s original 8031/8051/8751 specification, Figure 3.

Power and internal code selection

Required

Power VCC from a regulated 5 V supply (±5%). Place a 100 nF ceramic bypass between VCC and VSS. The high strap on EA selects the installed mask ROM at reset address 0000h.

100 nF between VCC rail and GroundVCC rail100 nFGround

Bench checks

  • Confirm the package pin 1 mark before applying power and measure VCC relative to ground at the IC.
  • Use a 100 nF X7R capacitor rated at least 16 V as the local high-frequency bypass. Keep its loop short.
  • Confirm the on-chip mask ROM contains the intended startup code before selecting internal execution.

Intel MCS-51 User’s Manual (1981), pp. 6-1–6-4

Connection scenarios

Pull up an open-drain Port 0 output

Use P0.0 as a slow open-drain output during internal execution. Write 0 to pull it low and 1 to release it. Connect the pull-up to the same VCC rail.

R2 10 kΩ between VCC rail and GPIO outputVCC railR2 10 kΩGPIO output

Bench checks

  • At 5.25 V and with R2 at its 9.9 kΩ minimum, the resistor limits sink current to 0.54 mA and dissipates under 2.8 mW. Use 10 kΩ ±1%, rated at least 1/8 W.
  • At 100 pF total capacitance, the maximum nominal RC time constant with resistor tolerance is about 1.01 µs. Verify rise time against the actual receiving input and its timing.
  • Leave this connection on a GPIO only while firmware avoids external memory cycles that use Port 0.

Intel MCS-51 Family User’s Manual (1994), chapter 3, Figure 4, and Intel 1981 p. 6-3

DIP-40 wiring map

Highlighted contacts are used in the required step or selected circuit. Select a contact to inspect it.

Top view. The notch is up, pin 1 is upper left and pin 40 is upper right.
Selected pin details

39 · P0.0

Bidirectional · Bidirectional

Open-drain GPIO. Latch 1 releases the output, so add an external pull-up when a driven HIGH is required. AD0 carries the multiplexed low address bit and data bit during external memory cycles, with an internal pull-up for bus operation.

After reset · Latch = 1. High impedance in GPIO mode.

Intel MCS-51, 1981 pp. 6-1–6-2 and 1994 pp. 3-6–3-7, 3-26–3-27

Electrical limits · Pin in the reference

Models and documents

This map covers the original Intel 8051 in the documented 40-pin DIP. Intel’s 8051AH, 80C51, ROMless 8031 and EPROM 8751 have their own electrical or programming specifications. The early original-device electrical table is marked preliminary.

Intel 8051
Original HMOS device, DIP-40. 4 KiB factory mask ROM, 128 B RAM, 32 port pins, two 16-bit timers, five interrupt sources and a full-duplex serial port.