Msg: 5332 *Conference*

08-16-94 15:41:49

From: RON WIESEN

To : COMET _

Subj: REPLY TO MSG #5319 (UNDOCUMENTED 80C85 OPCODES)

You are correct.  DEHL byte has an action of DE<=HL+byte.  My errata sheet
shows this error and two others in the ROM2 manual.  It's shown below.
 
ERRATA FOR ROM2 MANUAL
----------------------------------------------------------------
p23  DEHL byte  action DE<=HL+byte
 
p24  RST  n     action SP<=SP-2, w[SP]<=PC+1, PC<=n*8
 
p21  (An LDAX B instruction would set the A register to 50 hex.)
----------------------------------------------------------------
 
On page 24 of ROM2 manual, "RST n" action is in error.  See errata above.
Perhaps this error is your concern about "RST V (hex CB) opcode" of your
Msg#6071.  My manual only lists "RST n" and it does not list any hex codes at
all.  So maybe you're mixing info from a 8085 microprocessor manual?  Manuals
aside, "RST n" acts as a CALL instruction but with one of eight fixed
addresses.  Where n is 0, 1, 2, 3, 4, 5, 6, or 7, the respective called address
is 0, 8, 10, 18, 20, 28, 30, or 38 (hex).  Although not directly related to
"RST n", other intermingled or nearby fixed addresses that are notable in the
Model T are: 24 hex  8085 low power trap - A non maskable interrupt vector. 2C
hex  "RST 5.5" - data present at Bar Code port.  Another interrupt vector. 34
hex  "RST 6.5" - data present at UART.  Another interrupt vector. 3C hex  "RST
7.5" - timer (real-time) interrupt vector.  Model T op system sets up timer for
4 microsecond intervals.
 
So what's this "RST V" instruction you speak of?  Sounds like some kind of
interrupt vector ("RST 8.0" if you catch my drift) that might relate to
"Voltage" I guess.  You say it's op code is CB hex, so what manual gave you
that info?
 
Concerning flags, page 22 of the ROM2 manual indicates flag bit positions only
as they appear in memory (stack) after a PUSH PSW.  I believe I read a
microprocessor manual that said the "Flag Register" within the 8085 has the
bits in a different order.  Again, my memory ain't the greatest!  But I recall
that all eight bits of the Flag Register were documented.  I'll cruise through
my manuals and see what I find.
 
Anyway, you now have al my errata for the ROM2 manual and I have the mysterious
"RST V" to research.  Talk to you later.