diff --git a/I1620/i1620_cpu.c b/I1620/i1620_cpu.c
index d047d515..75862d21 100644
--- a/I1620/i1620_cpu.c
+++ b/I1620/i1620_cpu.c
@@ -2170,7 +2170,7 @@ cpuio_inp = 1;
 cpuio_opc = op;
 cpuio_cnt = 0;
 if (uptr != NULL)
-    sim_activate_after_abs (uptr, 1000000/uptr->wait);
+    DEFIO_ACTIVATE_ABS (uptr);
 return SCPE_OK;
 }
 
diff --git a/I1620/i1620_defs.h b/I1620/i1620_defs.h
index a0a68995..d03e2cc1 100644
--- a/I1620/i1620_defs.h
+++ b/I1620/i1620_defs.h
@@ -240,7 +240,9 @@ enum opcodes {
 
 #define DEV_DEFIO       (1 << (DEV_V_UF + 0))
 
-#define DEFIO_CPS       50                  /* Default Characters per Second */
+#define DEFIO_CPS       u4                  /* Default Characters per Second field */
+#define DEFIO_ACTIVATE(uptr) ((uptr)->DEFIO_CPS) ? sim_activate_after (uptr, 1000000/(uptr)->DEFIO_CPS) : sim_activate (uptr, (uptr)->wait)
+#define DEFIO_ACTIVATE_ABS(uptr) ((uptr)->DEFIO_CPS) ? sim_activate_after_abs (uptr, 1000000/(uptr)->DEFIO_CPS) : sim_activate_abs (uptr, (uptr)->wait)
 
 /* Function declarations */
 
diff --git a/I1620/i1620_pt.c b/I1620/i1620_pt.c
index 5043bd75..09dac0f3 100644
--- a/I1620/i1620_pt.c
+++ b/I1620/i1620_pt.c
@@ -74,13 +74,14 @@ t_stat ptp_num (void);
 */
 
 UNIT ptr_unit = {
-    UDATA (&ptr_svc, UNIT_SEQ+UNIT_ATTABLE+UNIT_ROABLE, 0), DEFIO_CPS
+    UDATA (&ptr_svc, UNIT_SEQ+UNIT_ATTABLE+UNIT_ROABLE, 0), SERIAL_OUT_WAIT
     };
 
 REG ptr_reg[] = {
     { FLDATA (BIN, ptr_mode, 0) },
     { DRDATA (POS, ptr_unit.pos, T_ADDR_W), PV_LEFT },
-    { DRDATA (CPS, ptr_unit.wait, 24), PV_LEFT },
+    { DRDATA (TIME, ptr_unit.wait, 24), PV_LEFT },
+    { DRDATA (CPS, ptr_unit.DEFIO_CPS, 24), PV_LEFT },
     { NULL }
     };
 
@@ -100,13 +101,14 @@ DEVICE ptr_dev = {
 */
 
 UNIT ptp_unit = {
-    UDATA (&ptp_svc, UNIT_SEQ+UNIT_ATTABLE, 0), DEFIO_CPS
+    UDATA (&ptp_svc, UNIT_SEQ+UNIT_ATTABLE, 0), SERIAL_OUT_WAIT
     };
 
 REG ptp_reg[] = {
     { FLDATA (BIN, ptp_mode, 0) },
     { DRDATA (POS, ptp_unit.pos, T_ADDR_W), PV_LEFT },
-    { DRDATA (CPS, ptp_unit.wait, 24), PV_LEFT },
+    { DRDATA (TIME, ptp_unit.wait, 24), PV_LEFT },
+    { DRDATA (CPS, ptr_unit.DEFIO_CPS, 24), PV_LEFT },
     { NULL }
     };
 
@@ -268,7 +270,7 @@ if (cpuio_cnt >= MEMSIZE) {                             /* over the limit? */
     cpuio_clr_inp (uptr);                               /* done */
     return STOP_RWRAP;
     }
-sim_activate_after (uptr, 1000000/uptr->wait);          /* sched another xfer */
+DEFIO_ACTIVATE (uptr);                                  /* sched another xfer */
 if ((uptr->flags & UNIT_ATT) == 0)                      /* not attached? */
     return SCPE_UNATT;
 
@@ -425,7 +427,7 @@ if ((cpuio_opc != OP_DN) && (cpuio_cnt >= MEMSIZE)) {   /* wrap, ~dump? */
     cpuio_clr_inp (uptr);                               /* done */
     return STOP_RWRAP;
     }
-sim_activate_after (uptr, 1000000/uptr->wait);          /* sched another xfer */
+DEFIO_ACTIVATE (uptr);                                  /* sched another xfer */
 if ((uptr->flags & UNIT_ATT) == 0)                      /* not attached? */
     return SCPE_UNATT;
 
diff --git a/I1620/i1620_tty.c b/I1620/i1620_tty.c
index 02a5d78d..5a488dc1 100644
--- a/I1620/i1620_tty.c
+++ b/I1620/i1620_tty.c
@@ -90,7 +90,7 @@ t_stat tty_set_12digit (UNIT *uptr, int32 val, CONST char *cptr, void *desc);
 */
 
 UNIT tty_unit[] = {
-    { UDATA (&tto_svc, 0, 0), DEFIO_CPS },
+    { UDATA (&tto_svc, 0, 0), SERIAL_OUT_WAIT },
     { UDATA (&tti_svc, 0, 0), KBD_POLL_WAIT }
     };
 
@@ -99,7 +99,8 @@ REG tty_reg[] = {
     { FLDATA (FLAG, tti_flag, 0), REG_HRO },
     { DRDATA (COL, tto_col, 7) },
     { DRDATA (KTIME, tty_unit[UTTI].wait, 24), REG_NZ + PV_LEFT },
-    { DRDATA (CPS, tty_unit[UTTO].wait, 24), REG_NZ + PV_LEFT },
+    { DRDATA (TTIME, tty_unit[UTTO].wait, 24), REG_NZ + PV_LEFT },
+    { DRDATA (CPS, tty_unit[UTTO].DEFIO_CPS, 24), REG_NZ + PV_LEFT },
     { NULL }
     };
 
@@ -389,7 +390,7 @@ if ((cpuio_opc != OP_DN) && (cpuio_cnt >= MEMSIZE)) {   /* wrap, ~dump? */
     cpuio_clr_inp (uptr);                               /* done */
     return STOP_RWRAP;
     }
-sim_activate_after (uptr, 1000000/uptr->wait);          /* sched another xfer */
+DEFIO_ACTIVATE (uptr);                                  /* sched another xfer */
 
 switch (cpuio_opc) {                                    /* decode op */