HP 3000 III Series Manual page 186

System Microcode
Table 5-2. R-Bus Field Code Definitions
-----------
-
--I-----I---------------~-------------I
No Opera tion.
MREG 0011
NOP 1111
(No Oper a t ion)
, Field
1 1
Label and Name
1
Code
1
Des cr ipt ion I
- - - - - - - - - - - - - - - , - - 1 -------_._------------- - .. 1
I ,
1
I
The MREG R-Bus field code is used
I
to fetch a memory element that hap-I
pens to lie in a TOS register ,
(i •
e.,
E i s grea te r t han S
ttl).
P r i -
or to executing MREG, the value of
S min us Emus t be placed in the SPI
Register. During execution of MREG,
TNAME becomes the sum of NAME and
SPl{14:l5) and the R-Bus Register
is loaded as follows:
If TNAME
=
00 then R-BUS :
=
TROR
If TNAME
=
01 then R-BUS :
=
TRIR
If TNAME
=
10 then R-BU S :
=
TR2R
If TNAME
=
11 then R-BUS
:=
TR3R
Due to the pipeline affect, a TOS
register referenced in the Store
field of the preceding microin-
struction assumes the above TNAME.
PADD
(Pre-Adder)
0100 The 16-bit content of the Pre-Adder
is loaded into the R-Bus Register.
PL
0000 The 16-bit content of the PL lEg-
ister is loaded into the R-Bus Reg-
i ste r.
RA
1011 The RA R-Bus field code is used to
read the content of the first TOS
register (location S). SR must be
greate r than O. * Our ing execution,
TNAME becomes NAME and the R-Bus
Register is loaded as follows:
If TNAME
=
00
then R-BUS :
=
TROR
If TNAME
=
01 then R-BU S :
=
TRIR
If TNAME
=
10 then R-BUS
:=
TR2R
If TNAME
=
11 then R-BUS :
=
TR3R
*True only if RA:RD are being used as part of the stack. RA:RD
are used
by
the microprogram as scratch pad registers when not
used othe rw ise.
5-6