PROf'lPT 48

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PROf'lPT 48

THE I-lOST II1PORTANT RULE OF THUMB is ~co ensure when you operate the Prompt 48 that these three things are correct:

ACCESS HODE P2 HAP

LSN of P2

TIM~R INTERRUP~ DISABLED ON 'SINGLE-STEP' or 'WITH-BREAKPOINT HODE. To dei:Juc; timer routines, - theiG-ins-cpt JTF (Jump on Timer flag) command in the program loop.

MONI'l'(ll~ RE--rNTnY usrs NEXT AVAILABLE LEVEL OF THE STACK. I f user is not al>]are of thls and puts data immediately above his s-tack, the date will be ^II zapped ^{n •}

UPPER 15 BYTES OF 1st lK BLOCK (3FO-3FF) MUST BE RESERVED FOR RI> L~iTRY ceDE. 'J'his applies ^h7hetheT' iT;e---usel~s running - out-

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the-II( vJl"'i teable prosl'C'.]" memory or out of the lK on--boBPd pro:::-;. Prom prc)grarmning cOJnrnano. [7l (see command s truci~ul'C )

autoffiat~cally progra~s this re-e~try code into tl10se 16 bytes.

Pl'om programming conTland [3] does not.

ANL ^~US ,A and ORL BUS ,ft. ARE NOT SUPPOHTED EXCEPT IN ACCESS r-lOm:; 3 AND THEN ONLY HJ 'G0 NO BREAK ^{I •}

OUTL BUS.A CAN ONLY BE USED IN ACCESS MODE 0 OR 3.

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Page 2

LIMITED USE OF INS A, BUS. This one takes some explanation.

At the chip level, the MCS48 BUS port was designed to work in one of the following configurations but not in combination of these modes.

CONfIGURATION 1) Bi-Directional 2) Uni-Directional

3) Uni-Directional

IN/OUT both out 1n TABLE 2

COMMAND MOVX OUTL INS

In all 3 configurations, command RD and WR 1S produced but is not generally used on the INS and OUTL.

PROMPT 48 supports the first and second configurations compl€tely:

bi-directional, using access mode 1 or 4 and uni-directional out- put using access mode 0 or 3. The INS cormnand is basically not

supported by the PROMPT 48 but i t can be used by doing the following:

1) 2) 3)

USE ACCESS .SET (DRIVE (explained STROBE THE

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HODE HIGH) 1n #8 DATA

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PORT 2 LINE 2 OR 3 belmv)

ONTO THE BUS vJITH THE

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Figure 1 - Strobed Data Input

RD LINE (Figure

USER1S EXTERNAL SYSTEM

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Figure ^° 2 shows the reason for the above steps. Access mode 1 or 4 enables a bi-directional driver and tri-states a latch that holds the data on an OUTL BUS,A command. Setting P22 or P23 deselects internal PROMPT48 memories. Data must be strobed onto the bus or else the in~ts would fight the 8216 drivers which are driving out when RD is inactive.

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Figure 2 - DATA PATH WITHIN PROJ1PT48 USING INS A, BUS

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Page 4

P2 MAPPING. The lines of Port 2 must be designated on a pin by pin basis as to their direction. This is done with the P2 map command. The default condition is 'output'. The follow- ing items need to be considered:

P23-27 MAY BE MAPPED 'INPUT' OR 'OUTPUT' REGARDLESS OF ACCESS MODE. These pins are wired directly from the execution CPU to JI interface so the only cri- terion is what device the user attaches to the pin.

P20-23 MAPPING IS DETERMINED BY ACCESS. This re- quires explanation on a mode-by-mode basis:

NODES 0,2, OR 5 - HAP P20-23 AS OUTPUT P20-23 are used by the monitor to select various internal memories of the PROMPT 48 and therefore must not be affected by input devices. Referring to Figure 3, we can see the data path is P2,H,J,K. If P20-23 is mapped in- ppt, data Path Jl, A, D, G, H could foul things up.

MODE 1 or 4 - MAPPING IS 'DON'T CARE'

P20-23 are used by the user to select various external memories, 10 chips, and/or 8243 Port Expander chips he may have connected to Jl.

Being select lines, their function will always be output except if using an 8243 Port Expander.

In Figure 3 the path is H, G, B, E, Jl. The P20-23 mapping mechanism is actually bypassed in these modes and is therefo"re immaterial.

If i t is mapped as output, the contents are saved by the monitor during debug. If using an 8243, on a MOVD A,Pn command, the path switches to Jl, F, B, G, H. "

MODE 3 - HAPPING MAY BE INPUT OR OUTPUT AS THE USER REQU..l.RES

In this mode we are running a <lK program on- board the CPU. With INPUT mapping the path is Jl, A, D, G and H. With OUTPUT ~apping the path is P2, H, J, C, A, Jl. You might notice that if the monitor takes control (due either to single- step, with-break, or monitor interrupt pressed) the last data on the 4-bit latch is held and the P2-map is temporarily switched to OUTPUT. Again, this is to prevent possible innut lines from

affecting the internal memory ~elect lines.

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rigure 3 - PROMPT48 PORT 2 BUS· STRUCTURE

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Page 6

RAM AND 10 SELECTION. On MCS 48 systems, the MOVX command is used for data and 10 transfers with RO or Rl as a pointer.

The addressing capability is then limited to 1 page (256).

This is expanded to 4K by using P20-23, decoded to 16 page

selects. Internally the PROMPT48 requires the first lK addresses, i.e. P22 and 23 low. There are 2 consequences of this:

a) To access the 256 byte user ram that's inside the PROMPT48, the user program must output O's to P22 and 23. (drive low). P20 and P2l are 'don't care'.

EARLY VERSIONS OF PROI1PTl.J 8:

a) EXHIBIT GLITCHES ON ,PORT 2 AND BUS

b) PERFORM READS ON EXPANSION BUS WHEN MONITOR IS OPERATING.

On some 10 chips this Cdn be a problem.

c) 'HANGS UP' HHEN 'USER INT' KEY HELD \\1HILE SINGLE-STEPPING THROUGH THE PROGRAM.

d) DON ^f T ALLOv] USER PROGRAMS TO HRITE TO DATA RAM UNDER ACCESS MODES 0 OR 1. If i t works under access mode 2, 'then you have this problem. - -First check that LSN of

P2 < 3.

All of the above have been fixed by ECO. Contact the factory if you are experiencing problems.

TTY AND CRT PERIPHERALS ARE USED ONLY fOR DUMPING OR READING PAPER TAPE. The keyboard input lS not a substi-tute for the keypad on the PROMPT48.

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YOU MAY CONNECT A 40-PIN SOCKET TO JI AND RUN A PROTOTYPE WITH THE PROMPT48. All of the major

SS (pin 5») EA (pin 7~ Vcc (pin 40») This does not make i t an ICE module.

and no trace or symbolic debug.

pins are wired to JI except and VDD (pin 26). Caution:

It has limited breakpoints

GROSS SPEED DEGRADATION OCCURS WHEN 'GO WITH BREAKPOINTS'.

This is due basically because the operation is a replica of single-stepping. This means that after every instruction the monitor re-takes control, saves the processor state) checks the PC against the eight breakpoints, then restores the processor state and goes back to the USer mode. - If your program has

timing loops in it, you can easily think the processor has 'gone out to lunch'.

WHEN USING PROMPT48 SYSTEM CALLS, DO NOT 'GO WITH SGL. STEP' OR 'GO WITH BREAKPOINT'. The monitor is like a lot of us; i t does not handle self-examination very well!

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