diff --git a/src/instruction.c b/src/instruction.c
index 40b4824..7654e1e 100644
--- a/src/instruction.c
+++ b/src/instruction.c
@@ -220,3 +220,23 @@ instruction_data_read_1(rk65c02emu_t *e, instrdef_t *id, instruction_t *i)
 	return rv;
 }
 
+/* put value onto the stack */
+void
+stack_push(rk65c02emu_t *e, uint8_t val)
+{
+	bus_write_1(e->bus, STACK_START+e->regs.SP, val);
+	e->regs.SP--;
+}
+
+/* pull/pop value from the stack */
+uint8_t
+stack_pop(rk65c02emu_t *e)
+{
+	uint8_t val;
+
+	val = bus_read_1(e->bus, STACK_START+e->regs.SP);
+	e->regs.SP++;
+
+	return val;
+}
+
diff --git a/src/rk65c02.h b/src/rk65c02.h
index 6b0e698..8c748f8 100644
--- a/src/rk65c02.h
+++ b/src/rk65c02.h
@@ -28,7 +28,10 @@ struct reg_state {
 #define P_SIGN_OVERFLOW 0x40
 #define P_NEGATIVE 0x80
 
-#define NEGATIVE P_NEGATIVE
+#define NEGATIVE P_NEGATIVE /* sign bit */
+
+#define STACK_START 0x0100
+#define STACK_END 0x01FF
 
 typedef struct reg_state reg_state_t;