diff --git a/src/Cpu.php b/src/Cpu.php
index 7109231..03e9759 100644
--- a/src/Cpu.php
+++ b/src/Cpu.php
@@ -28,11 +28,11 @@ class Cpu {
     }
 
     public function popU8(): int {
-        return $this->io->read($this->state->sPage | $this->state->s--);
+        return $this->io->read($this->state->sPage | $this->state->s++);
     }
 
     public function pushU8(int $value): void {
-        $this->io->write($this->state->sPage | $this->state->s++, $value);
+        $this->io->write($this->state->sPage | $this->state->s--, $value);
     }
 
     public function popU16(): int {
@@ -64,13 +64,19 @@ class Cpu {
             return;
         }
 
-        $vector = match($irq) {
-            CpuInterruptRequest::Maskable => self::IV_IRQ,
-            CpuInterruptRequest::NonMaskable => self::IV_NMI,
-            default => throw new RuntimeException('unexpected irq value')
-        };
+        $pc = $this->state->pc;
 
-        $this->pushU16($this->state->pc);
+        if($irq === CpuInterruptRequest::Break) {
+            $vector = self::IV_IRQ;
+            ++$pc;
+        } else
+            $vector = match($irq) {
+                CpuInterruptRequest::Maskable => self::IV_IRQ,
+                CpuInterruptRequest::NonMaskable => self::IV_NMI,
+                default => throw new RuntimeException('unexpected irq value')
+            };
+
+        $this->pushU16($pc);
         $this->pushU8($this->state->p);
         $this->state->pc = $this->readIoU16($vector);
     }