Texas Instruments 990 Operation Manual page 45

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The second letter of a debug command represents the element on which an operation is
performed, and may be one of the following:
Second Letter
of Command
M
w
R
C
B
S
T
p
Element
The Memory element represents any RAM or ROM in the hardware system configura-
tion. If nonexistent memory is specified, an undefined bit pattern is returned.
The Workspace element represents the user program's current workspace registers,
registers 0 through 15. In a Find Word command, W represents
word.
The Registers element represents the user's program counter register, workspace pointer
register and status register.
In a Set Trace Region (SR) or Clear Trace Region (CR) command, R represents
region. A region is a memory area where there will occur a trace of statements exe-
cuted when running under Instruction Trace. Associated with each region is its index
(a number from 0 to 3), trace type, mode of execution (single step or continuous
run), and, optionally, variables to be traced.
The CRU element represents the Communications Register Unit of the 990 Computer.
The data on the CRU input lines and the input line numbers may be displayed, and
the data on the CRU output lines may be modified.
The Breakpoint element represents the four program counter (PC) breakpoints. Asso-
ciated with each breakpoint is its index (a number from 0 to 3), a program counter
value, a reference counter (optional) and a snapshot index (optional). The user's pro-
gram counter, workspace pointer and status register are automatically printed along
with the breakpoint index number. If a snapshot was associated with the breakpoint
at definition time, then the snapshot indicated by the snapshot index is also printed.
Breakpoints are detected before instruction execution.
In a Find Byte (FB) command, B represents byte.
The Snapshot element represents a four-element vector of program displays. Each dis-
play is characterized by a range of workspace registers and a range of memory. When-
ever a snapshot is invoked, the register and memory ranges are dumped to the
printer.
The Trace element is a four-element vector of trace types. Associated with each ele-
ment is an index and a string of characters indicating the type of trace. The Set Trace
Definition (ST) command modifies an existing trace type of the same index. When the
monitor is loaded, each element is assigned a default trace type. (For example, type 1
is PIWSEADEA: program counter, instruction and format, workspace pointer changes,
source and destination, effective addresses and their contents after execution.) The ST
command is available only if the Instruction Trace overlay is in memory.
The Protect element represents a write-protected region of memory.
The individual debug commands are described in paragraph 3.4.12 through 3.4.32.
3-7 Digital Systems Division .