diff --git a/PDP1/pdp1_clk.c b/PDP1/pdp1_clk.c
index 93fbd473..61715592 100644
--- a/PDP1/pdp1_clk.c
+++ b/PDP1/pdp1_clk.c
@@ -118,9 +118,8 @@ t_stat clk_reset (DEVICE *dptr)
 {
 if (clk_dev.flags & DEV_DIS) sim_cancel (&clk_unit);    /* disabled? */
 else {
-    sim_register_clock_unit (&clk_unit);                /* declare clock unit */
-    tmxr_poll = sim_rtcn_init (clk_unit.wait, TMR_CLK);
-    sim_activate_abs (&clk_unit, tmxr_poll);            /* activate unit */
+    tmxr_poll = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init timer */
+    sim_activate_after (&clk_unit, 1000000/CLK_TPS);    /* activate unit */
     }
 clk_cntr = 0;                                           /* clear counter */
 return SCPE_OK;
diff --git a/PDP11/pdp11_stddev.c b/PDP11/pdp11_stddev.c
index 8e686053..aa0e4450 100644
--- a/PDP11/pdp11_stddev.c
+++ b/PDP11/pdp11_stddev.c
@@ -471,7 +471,6 @@ return clk_dib.vec;
 
 t_stat clk_reset (DEVICE *dptr)
 {
-sim_register_clock_unit (&clk_unit);                    /* declare clock unit */
 if (CPUT (HAS_LTCR))                                    /* reg there? */
     clk_fie = clk_fnxm = 0;
 else {
@@ -481,8 +480,8 @@ else {
 clk_tps = clk_default;                                  /* set default tps */
 clk_csr = CSR_DONE;                                     /* set done */
 CLR_INT (CLK);
-sim_rtcn_init (clk_unit.wait, TMR_CLK);                 /* init line clock */
-sim_activate (&clk_unit, clk_unit.wait);                /* activate unit */
+tmr_poll = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init line clock */
+sim_activate_after (&clk_unit, 1000000/clk_tps);        /* activate unit */
 tmr_poll = clk_unit.wait;                               /* set timer poll */
 tmxr_poll = clk_unit.wait;                              /* set mux poll */
 return SCPE_OK;
diff --git a/PDP8/pdp8_clk.c b/PDP8/pdp8_clk.c
index 1fcaca0c..08fe879e 100644
--- a/PDP8/pdp8_clk.c
+++ b/PDP8/pdp8_clk.c
@@ -141,12 +141,9 @@ switch (IR & 07) {                                      /* decode IR<9:11> */
 
 t_stat clk_svc (UNIT *uptr)
 {
-int32 t;
-
 dev_done = dev_done | INT_CLK;                          /* set done */
 int_req = INT_UPDATE;                                   /* update interrupts */
-t = sim_rtcn_calb (clk_tps, TMR_CLK);                   /* calibrate clock */
-tmxr_poll = t;                                          /* set mux poll */
+tmxr_poll = sim_rtcn_calb (clk_tps, TMR_CLK);           /* calibrate clock */
 sim_activate_after (uptr, 1000000/clk_tps);             /* reactivate unit */
 return SCPE_OK;
 }
@@ -155,16 +152,12 @@ return SCPE_OK;
 
 t_stat clk_reset (DEVICE *dptr)
 {
-int32 t;
-
-sim_register_clock_unit (&clk_unit);                    /* declare clock unit */
 dev_done = dev_done & ~INT_CLK;                         /* clear done, int */
 int_req = int_req & ~INT_CLK;
 int_enable = int_enable & ~INT_CLK;                     /* clear enable */
 if (!sim_is_running) {                                  /* RESET (not CAF)? */
-    t = sim_rtcn_init (clk_unit.wait, TMR_CLK);
-    sim_activate (&clk_unit, t);                        /* activate unit */
-    tmxr_poll = t;
+    tmxr_poll = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init 100Hz timer */
+    sim_activate_after (&clk_unit, 1000000/clk_tps);        /* activate 100Hz unit */
     }
 return SCPE_OK;
 }
diff --git a/VAX/vax610_stddev.c b/VAX/vax610_stddev.c
index 58f10b46..1436f32a 100644
--- a/VAX/vax610_stddev.c
+++ b/VAX/vax610_stddev.c
@@ -453,11 +453,10 @@ t_stat clk_reset (DEVICE *dptr)
 {
 int32 t;
 
-sim_register_clock_unit (&clk_unit);                    /* declare clock unit */
 clk_csr = 0;
 CLR_INT (CLK);
-t = sim_rtcn_init (clk_unit.wait, TMR_CLK);             /* init timer */
-sim_activate_abs (&clk_unit, t);                        /* activate unit */
+t = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init 100Hz timer */
+sim_activate_after (&clk_unit, 1000000/clk_tps);        /* activate 100Hz unit */
 tmr_poll = t;                                           /* set tmr poll */
 tmxr_poll = t * TMXR_MULT;                              /* set mux poll */
 return SCPE_OK;
diff --git a/VAX/vax630_stddev.c b/VAX/vax630_stddev.c
index 3b264450..aa390704 100644
--- a/VAX/vax630_stddev.c
+++ b/VAX/vax630_stddev.c
@@ -396,11 +396,10 @@ t_stat clk_reset (DEVICE *dptr)
 {
 int32 t;
 
-sim_register_clock_unit (&clk_unit);                    /* declare clock unit */
 clk_csr = 0;
 CLR_INT (CLK);
-t = sim_rtcn_init (clk_unit.wait, TMR_CLK);             /* init timer */
-sim_activate_abs (&clk_unit, t);                        /* activate unit */
+t = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init 100Hz timer */
+sim_activate_after (&clk_unit, 1000000/clk_tps);        /* activate 100Hz unit */
 tmr_poll = t;                                           /* set tmr poll */
 tmxr_poll = t * TMXR_MULT;                              /* set mux poll */
 return SCPE_OK;
diff --git a/VAX/vax730_stddev.c b/VAX/vax730_stddev.c
index e61909c5..b06d781e 100644
--- a/VAX/vax730_stddev.c
+++ b/VAX/vax730_stddev.c
@@ -757,9 +757,8 @@ return;
 
 t_stat clk_reset (DEVICE *dptr)
 {
-sim_register_clock_unit (&clk_unit);                    /* declare clock unit */
-tmr_poll = sim_rtcn_init (clk_unit.wait, TMR_CLK);      /* init 100Hz timer */
-sim_activate_abs (&clk_unit, tmr_poll);                 /* activate 100Hz unit */
+tmr_poll = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init 100Hz timer */
+sim_activate_after (&clk_unit, 1000000/clk_tps);        /* activate 100Hz unit */
 tmxr_poll = tmr_poll * TMXR_MULT;                       /* set mux poll */
 if (clk_unit.filebuf == NULL) {                         /* make sure the TODR is initialized */
     clk_unit.filebuf = calloc(sizeof(TOY), 1);
diff --git a/VAX/vax750_stddev.c b/VAX/vax750_stddev.c
index 8f65f6a6..a61e9a71 100644
--- a/VAX/vax750_stddev.c
+++ b/VAX/vax750_stddev.c
@@ -792,9 +792,8 @@ return;
 
 t_stat clk_reset (DEVICE *dptr)
 {
-sim_register_clock_unit (&clk_unit);                    /* declare clock unit */
-tmr_poll = sim_rtcn_init (clk_unit.wait, TMR_CLK);      /* init 100Hz timer */
-sim_activate_abs (&clk_unit, tmr_poll);                 /* activate 100Hz unit */
+tmr_poll = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init 100Hz timer */
+sim_activate_after (&clk_unit, 1000000/clk_tps);        /* activate 100Hz unit */
 tmxr_poll = tmr_poll * TMXR_MULT;                       /* set mux poll */
 if (clk_unit.filebuf == NULL) {                         /* make sure the TODR is initialized */
     clk_unit.filebuf = calloc(sizeof(TOY), 1);
diff --git a/VAX/vax780_stddev.c b/VAX/vax780_stddev.c
index 8254c119..4694d54f 100644
--- a/VAX/vax780_stddev.c
+++ b/VAX/vax780_stddev.c
@@ -734,9 +734,8 @@ if (SCPE_OK == sim_activate_after (&tmr_unit, usecs))
 
 t_stat clk_reset (DEVICE *dptr)
 {
-sim_register_clock_unit (&clk_unit);                    /* declare clock unit */
-tmr_poll = sim_rtcn_init (clk_unit.wait, TMR_CLK);      /* init 100Hz timer */
-sim_activate (&clk_unit, tmr_poll);                     /* activate 100Hz unit */
+tmr_poll = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init 100Hz timer */
+sim_activate_after (&clk_unit, 1000000/clk_tps);        /* activate 100Hz unit */
 tmxr_poll = tmr_poll * TMXR_MULT;                       /* set mux poll */
 if (clk_unit.filebuf == NULL) {                         /* make sure the TODR is initialized */
     clk_unit.filebuf = calloc(sizeof(TOY), 1);
diff --git a/VAX/vax860_stddev.c b/VAX/vax860_stddev.c
index 00fccd09..c656349e 100644
--- a/VAX/vax860_stddev.c
+++ b/VAX/vax860_stddev.c
@@ -856,9 +856,8 @@ return;
 
 t_stat clk_reset (DEVICE *dptr)
 {
-sim_register_clock_unit (&clk_unit);                    /* declare clock unit */
-tmr_poll = sim_rtcn_init (clk_unit.wait, TMR_CLK);      /* init 100Hz timer */
-sim_activate (&clk_unit, tmr_poll);                     /* activate 100Hz unit */
+tmr_poll = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init 100Hz timer */
+sim_activate_after (&clk_unit, 1000000/clk_tps);        /* activate 100Hz unit */
 tmxr_poll = tmr_poll * TMXR_MULT;                       /* set mux poll */
 if (clk_unit.filebuf == NULL) {                         /* make sure the TODR is initialized */
     clk_unit.filebuf = calloc(sizeof(TOY), 1);
diff --git a/VAX/vax_stddev.c b/VAX/vax_stddev.c
index ca9c6196..97db3661 100644
--- a/VAX/vax_stddev.c
+++ b/VAX/vax_stddev.c
@@ -556,12 +556,11 @@ t_stat clk_reset (DEVICE *dptr)
 {
 int32 t;
 
-sim_register_clock_unit (&clk_unit);
 clk_csr = 0;
 CLR_INT (CLK);
 if (!sim_is_running) {                                  /* RESET (not IORESET)? */
-    t = sim_rtcn_init (clk_unit.wait, TMR_CLK);         /* init timer */
-    sim_activate_after (&clk_unit, 1000000/clk_tps);    /* activate unit */
+    t = sim_rtcn_init_unit (&clk_unit, clk_unit.wait, TMR_CLK);/* init 100Hz timer */
+    sim_activate_after (&clk_unit, 1000000/clk_tps);    /* activate 100Hz unit */
     tmr_poll = t;                                       /* set tmr poll */
     tmxr_poll = t * TMXR_MULT;                          /* set mux poll */
     }