diff options
Diffstat (limited to 'src/devices/machine/mc146818.cpp')
-rw-r--r-- | src/devices/machine/mc146818.cpp | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/src/devices/machine/mc146818.cpp b/src/devices/machine/mc146818.cpp index 8780643c2e3..254fa8a23b2 100644 --- a/src/devices/machine/mc146818.cpp +++ b/src/devices/machine/mc146818.cpp @@ -582,8 +582,11 @@ WRITE8_MEMBER( mc146818_device::write ) case REG_A: // top bit of A is read only - m_data[REG_A] = data & ~REG_A_UIP; - update_timer(); + if ((data ^ m_data[REG_A]) & ~REG_A_UIP) + { + m_data[REG_A] = data & ~REG_A_UIP; + update_timer(); + } break; case REG_B: |