Z80系统接地故障排查：ESP32调试地址随机跳变问题

我正在开发一款Z80系统，核心配置如下：

• 3片74HC138地址扩展芯片
• 1片RAM芯片
• 20MHz内部时钟模块
• 40针外部连接接口
• 配备手动时钟切换开关，可在内部20MHz时钟与外部ESP32时钟间切换
• 电路板采用细漆包铜线焊接

用ESP32调试时，运行向数据总线写入0x00、读取地址并串口打印的代码后出现异常：地址随机跳变，但触碰GND时地址能正常递增，推测核心问题是电路板接地不良。

硬件相关图示 #

Z80系统原理图 #

Z80与ESP32连接图 #

ESP32调试代码 #

#include <Arduino.h>

int pinAddress[] = {17, 5, 18, 19};
int pinData[] = {13, 12, 14, 27, 26, 25, 33, 32};
int pinClock = 16;

void writeData(byte data)
{
  for (int i = 0; i < sizeof(pinData) / sizeof(pinData[0]); i++)
  {
    digitalWrite(pinData[i], (data << i) & 1);
  }
}

byte readAddress()
{
  byte addr;
  for (int i = 0; i < sizeof(pinAddresss) / sizeof(pinAddresss[0]); i++)
  {
    addr |= digitalRead(pinAddresss[i]) << i;
  }

  return addr;
}

void setup()
{
  Serial.begin(115200);
  pinMode(pinClock, OUTPUT);

  for (int i = 0; i < sizeof(pinAddresss) / sizeof(pinAddresss[0]); i++)
  {
    pinMode(pinAddresss[i], INPUT);
  }

  for (int i = 0; i < sizeof(pinData) / sizeof(pinData[0]); i++)
  {
    pinMode(pinData[i], OUTPUT);
  }

  writeData(0x00);
}

void loop()
{
  digitalWrite(pinClock, HIGH);
  delay(250);
  digitalWrite(pinClock, LOW);
  delay(250);

  Serial.println("Address: 0b" + String(readAddress(), BIN));
}

ESP32串口输出（异常示例） #

Address: 0b1111
Address: 0b1111
Address: 0b1111
Address: 0b0
Address: 0b0
Address: 0b0
Address: 0b0
Address: 0b0
Address: 0b0
Address: 0b0
Address: 0b0
Address: 0b0
Address: 0b1
Address: 0b1
Address: 0b1
Address: 0b1
Address: 0b1
Address: 0b1
Address: 0b1
Address: 0b1
Address: 0b10
Address: 0b10
Address: 0b1
Address: 0b1
Address: 0b11
Address: 0b11
Address: 0b11
Address: 0b11
Address: 0b11
Address: 0b11
Address: 0b11
Address: 0b11
Address: 0b1100
Address: 0b1100
Address: 0b10
Address: 0b10
Address: 0b1101
Address: 0b1101
Address: 0b1101
Address: 0b1101
Address: 0b1101
Address: 0b1101
Address: 0b1101
Address: 0b1101
Address: 0b110
Address: 0b110
Address: 0b11
Address: 0b11
Address: 0b111
Address: 0b111
Address: 0b111
Address: 0b111
Address: 0b111
Address: 0b111
Address: 0b111
Address: 0b111
Address: 0b0
...

问题分析推测 #

触碰GND时地址恢复正常，说明系统存在接地阻抗过高或单点接地不良的情况。细漆包铜线焊接可能导致接地路径电阻过大，在20MHz高频时钟下容易产生信号干扰，造成地址总线电平不稳定、随机跳变。当触碰GND时，相当于人为提供了更低阻抗的接地路径，抑制了干扰，使地址信号恢复稳定。

内容的提问来源于stack exchange，提问作者Miguel Magno