diff --git a/PDP10/ka10_pd.c b/PDP10/ka10_pd.c
index 2aeaeed..d428cec 100644
--- a/PDP10/ka10_pd.c
+++ b/PDP10/ka10_pd.c
@@ -42,14 +42,24 @@
 #define PD_DEVNUM       0500
 #define PD_OFF          (1 << DEV_V_UF)
 
+#define PIA_CH          u3
+
+#define PIA_FLG         07
+#define CLK_IRQ         010
+
+#define TMR_PD          3
+
+int pd_tps =            60;
+
 t_stat         pd_devio(uint32 dev, uint64 *data);
 const char     *pd_description (DEVICE *dptr);
+t_stat         pd_srv(UNIT *uptr);
 t_stat         pd_set_on(UNIT *uptr, int32 val, CONST char *cptr, void *desc);
 t_stat         pd_set_off(UNIT *uptr, int32 val, CONST char *cptr, void *desc);
 t_stat         pd_show_on(FILE *st, UNIT *uptr, int32 val, CONST void *desc);
 
 UNIT                pd_unit[] = {
-    {UDATA(NULL, UNIT_DISABLE, 0)},  /* 0 */
+    {UDATA(pd_srv, UNIT_IDLE|UNIT_DISABLE, 0)},  /* 0 */
 };
 DIB pd_dib = {PD_DEVNUM, 1, &pd_devio, NULL};
 
@@ -91,6 +101,21 @@ t_stat pd_devio(uint32 dev, uint64 *data)
         else
             *data = pd_ticks();
         break;
+    case CONI:
+        *data = (uint64)(pd_unit[0].PIA_CH & (CLK_IRQ|PIA_FLG));
+        break;
+    case CONO:
+        pd_unit[0].PIA_CH &= ~(PIA_FLG);
+        pd_unit[0].PIA_CH |= (int32)(*data & PIA_FLG);
+        if (pd_unit[0].PIA_CH & PIA_FLG) {
+            if (!sim_is_active(pd_unit))
+                sim_activate(pd_unit, 10000); 
+        }
+        if (*data & CLK_IRQ) {
+            pd_unit[0].PIA_CH &= ~(CLK_IRQ);
+            clr_interrupt(PD_DEVNUM);
+        }
+        break;
     default:
         break;
     }
@@ -98,6 +123,23 @@ t_stat pd_devio(uint32 dev, uint64 *data)
     return SCPE_OK;
 }
 
+t_stat
+pd_srv(UNIT * uptr)
+{
+    int32 t;
+
+    t = sim_rtcn_calb (pd_tps, TMR_PD);
+    sim_activate_after(uptr, 1000000/pd_tps);
+    if (uptr->PIA_CH & PIA_FLG) {
+        uptr->PIA_CH |= CLK_IRQ;
+        set_interrupt(PD_DEVNUM, uptr->PIA_CH);
+    } else
+        sim_cancel(uptr);
+
+    return SCPE_OK;
+}
+
+
 const char *pd_description (DEVICE *dptr)
 {
     return "Paul DeCoriolis clock";