Alto Hardware Manual
Section
3:
Emulator
21
R37[14-1S]
o Off.
1 Normal mode. Every 38.08 microseconds, test to see
if
(R37
AND
TIMEMASK)=ITIIME
(on Alto I,
TIMEMASK=177700B;
on
Alto II, the
proper
value for
TIMEMASK
is
7774B,
but version
23
of
Alto II microcode uses a
value
of
7700B).
If
they are equal, cause an interrupt on
the
channel
specified by
ITIBITS.
Store the current state
of
the
EIA
interface
in
ITQUAN,
and set
R37[14-1S]
to zero.
The
state
of
the
EIA
interface is bit IS
of
location
EIALOC
(17770lB) in page
377B.
This bit
is
0
if
the line
is
spacing, 1
if
it
is
marking.
2
Same
as
O.
3 Every
38.08
microseconds, check the state
of
the.
EIA
line by reading
EIALOC.
If
the line
is
marking
(EIALOC
is
non zero), do nothing.
If
the line is
spacing, cause an interrupt
on
the channel specified
by
ITIBITS.
Store
the
current value
of
R37
in
ITQUAN,
and set
R37[14-1S]
to zero.
The intention
is
that a program which does
EIA
input can use mode 3 to monitor the line for
the
arrival
of
a character, and can then use mode 1 to time the center
of
each bit.
By
storing
the
state
of
the line, the interrupt latency
can
be
as
much as 1
bit
time without errors.
JMPRAM
610l0B
Jump to
RAM:
(see section
8.S
for details)
RDRAM
Switches the emulator task micro PC to another microinstruction
bank
ih
ROM
or
RAM
. The next
emulator microinstruction will be determined from the value
in
ACI
(mod
1024) -- see
the
discussion
of
bank switching in section
8.4.
. .
61011B
Read
RAM:
(see section 8.5 for details)
Reads· the control
RAM
halfword addressed
by
ACI
into
ACO.
Note:
In
Alto lIs running microcode version 2, this instruction does
not
work reliably
if
the
Ethernet interface
is
running.
WRTRAM
610l2B Write
RAM:
(see section
8.S
for details)
VERS
Writes
ACO
into the high-order half
and
AC3
into the low-order
half
of
the control
RA.M
word
addressed by
ACl.
61014B
Version:
ACO
is
loaded with a number which
is
coded
as
follows:
bits
0-3
Alto engineering number
00r1
Alto I
2 Alto II
3 Alto II with extended memory
bits
4-7
Alto build number.
bits
8-lS Version number
of
the microcode.
This instruction permits programs to know the differences among various kinds
of
Altos. Use
of
the Alto build number (bits 4-7) has been abandoned; its contents are undefined.
The
two
flavors
of
Alto maintain separate enumerations
of
microcode versions (see section 9 for some
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