First commit. Not tested!

README

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+74LS189 SRAM Emulator
+
+Written for use on an ATmega328 using Arduino 0022, this is an emulator designed to replicate the functionality of the 74LS189 16x4 SRAM. It is NOT pin-compatible, and CANNOT directly replace existing chips. Eventually other functionality will be added, such as serial access, but don't depend on that becoming available for some time.
+
+I have not tested it yet, as I don't have access to my Arduino. It is also not finished. Porting the code to other devices should be relatively simple, and if you do, get in touch with me and I can add it here.
+
+One last thing, I am not sure if this will be fast enough for high-speed designs, so use it (when its done) at your own risk.

_74ls198_emulator/_74ls198_emulator.pde

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+/*
+74LS189 Emulator
+
+This sketch is to replicate the funtions of the 74LS189 SRAM
+logic chip. This is not pin-compatible, but is feature-compatible.
+More features, such as serial access, will be available at a later
+date.
+
+Data is stored in an array for ease of use.
+*/
+
+boolean ram_data[16][4] = {
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0},
+  {0,0,0,0}
+};
+
+#define write_en 2
+#define chip_sel 3
+#define address 0
+#define data 1
+
+//Address inputs are 4-7
+boolean address_vals[] = {0, 0, 0, 0};
+byte address_byte;
+
+//Data inputs are 8-11
+boolean data_vals[] = {0, 0, 0, 0};
+
+//Inverted data outputs are 12-15
+boolean notdata[] = {0, 0, 0, 0};
+
+boolean write_en_state = 1;
+boolean chip_sel_state = 1;
+
+
+void setup(){
+  pinMode(write_en, INPUT);
+  pinMode(chip_sel, INPUT);
+
+  for(byte address_pin = 4; address_pin < 8; address_pin++){
+    pinMode(address_pin, INPUT);
+  }
+
+  for(byte data_in = 8; data_in < 12; data_in++){
+    pinMode(data_in, INPUT);
+  }
+
+  for(byte data_out = 12; data_out < 16; data_out++){
+    pinMode(data_out, OUTPUT);
+  }
+}
+
+void loop(){
+  chip_sel_state = digitalRead(chip_sel);
+  write_en_state = digitalRead(write_en);
+
+  if(chip_sel_state == 0){
+    readPins(address);
+
+    for(byte index = 0; index < 4; index++){
+      bitWrite(address_byte, index, address_vals[index]);
+    }
+
+    if(write_en_state == 0){
+      readPins(data);
+
+      for(byte index = 0; index < 4; index++){
+        ram_data[address_byte][index] = data_vals[index];
+        notdata[index] = !ram_data[address_byte][index];
+      }
+    }
+
+    for(byte output_pin = 12; output_pin < 16; output_pin++){
+      for(byte index = 0; index < 4; index++){
+        digitalWrite(output_pin, notdata[index]);
+      }
+    }
+  }
+}
+
+
+
+//This is a general purpose function to read pin states. To read
+//address pins, "type" should be "0". To read data pins, "type"
+//should be "1".
+void readPins(boolean type){
+  byte low_pin;
+  byte high_pin;
+  byte pin;
+  byte index;
+  boolean pin_state;
+
+  boolean temp_data[] = {0, 0, 0, 0};
+  boolean temp_index;
+
+  //Give pin-to-read variables values dependent on what pins we
+  //want to read
+  if(type == 0){
+    low_pin = 4;
+    high_pin = 8;
+  }
+
+  if(type == 1){
+    low_pin = 8;
+    high_pin = 12;
+  }
+
+
+  //Main for loop to read the pins requested, stores them in a
+  //temporary array
+  for(pin = low_pin; pin < high_pin; pin++){
+    for(index = 0; index < 4; index++){
+      pin_state = digitalRead(pin);
+      temp_data[index] = pin_state;
+    }
+  }
+
+
+  //Transfer the data into the correct array
+  if(type == 0){
+    for(temp_index = 0; temp_index < 4; temp_index++){
+      address_vals[temp_index] = temp_data[temp_index];
+    }
+  }
+
+  if(type == 1){
+    for(temp_index = 0; temp_index < 4; temp_index++){
+      data_vals[temp_index] = temp_data[temp_index];
+    }
+  }
+}