Input/Output Instructions; Overa" Characteristics; I/Ostatus Information - Xerox 560 Reference Manual

INPUT jOUTPUT INSTRUCTIONS
The I/o instruction set is comprised of eight instructions,
as listed below.
Instruction Name
Mnemonic
Start Input/Output SIO
Test Input/Output
TIO
Test Device TDY
Halt Input/Output HIO
Reset Input/Output RIO
Poll Processor POLP
Poll and Reset Processor
POLR
Acknowledge Input/Output Interrupt AIO
OVERALL CHARACTERISTICS
All I/o instructions are privi leged and can be performed
only when the basic processor (BP) is in either the master
or master-protected mode. If the BP attempts to execute
an I/o instruction when it is in the slave mode (bit 8 of
the current PSW is a 1), the instructi on is aborted at the
timl'> thl'> nnl'>rntinn c-nrll'> is rlpc-nrlprl nnrl thp RP trnns to
10-
. - - - - - - - - 1- - - -- - - - - - - - - - - - - - - I
cation X1401. Programs operating in the slave mode must
request I/O services from the System Monitor.
At the end of every I/O instruction, the condition code
bits represent a summary descri pti on of the resu I ts of the
I/O operation and conditions within the addressed I/O
subsystem. Specific condition code settings and meanings
(unique for each I/O instruction) are contained in the de-
tailed description for each I/O instruction.
All I/O instructions, except RIO, may request detailed
I/O status information. The type and amount of I/o status
information that may be requested is determined by the op-
eration code and the R field of the I/O instruction. The
R field also designates which general register(s) is to be
loaded with the requested information. (Refer to I/o Status
Informati on for further detai Is. )
I/O instructions are similar to other word-addressing in-
structions in that bits 15-31 may be modified by indirect
addressing and/or indexing. However, the final value of
these bits is not used as an effective virtual address for
memory reference. Instead, depending upon the I/o in-
struction, these bits are used as an extension to the opera-
tion code field, as an I/O address to select a particular
I/o subsystem, or they may be reserved. Further detai Is
of I/o instructions are illustrated in Figure 13 and de-
scribed in Table 13.
I/O STATUS INFORMATION
SIO, TIO, TDY, AND HIO INSTRUCTIONS
If the R field is coded with a 0, no status information is re-
quested nor loaded. If the R field is odd, one word of status
information is requested to be loaded into register R as spec-
ified by the R field. If the R field is even (not zero), two
words of status information are requested to be loaded into
registers Rand Ru 1 .
The following I/O status information may be loaded into
register R only when the R field is coded with an even
(nonzero) value.
The significance of each bit within register R is described
in Table 14.
The following I/O status information may be loaded into
register R if the R field is odd, or into register Ru 1 if the
R fi e I dis even and not zero.
The format of information within the specified general reg-
ister (R or Ru1) is shown below.
Device Status Byte. These eight bits (0-7) when loaded
into the specified general register provide status information
pertaining to the addressed device and device controller or
lOP. The significance of each bit when requested by an
SIO, TIO, and HIO instruction is described in Table 15.
The significance of these bits when requested by a TDY in-
struction is different and is described in the applicable
peripheral device reference manual.
Operational Status Byte. Bits 8-15 of the specified gen-
eral register (R or Ru1) indicate either the presence (1) or
absence (0) of various errors which may have occurred
during an I/O operation. The significance of the individ-
ual bits within the operational status byte are described
in Table 16.
Table 17 is the summary description of the Device Status
Byte and the Operational Status Byte.
Byte Count. Bits 16-31 of register Ru1 indicate the num-
ber of bytes that have to be transmitted to or from mem-
ory in the operation called for by the current I/o command
doubleword.
RIO INSTRUCTION
No status information is returned to the general registers
for an RIO instruction (the R field is ignored). Only con-
dition code bits (CC 1 - CC3) are set to reflect the I/O
conditions.
Input/Output Instructions 127