ENSC E-123: Homework D10: Counter as Peripheral

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1 Homework D10, Counter as Peripheral 1 REV 4 1 ; April 9, 2015 ENSC E-123: Homework D10: Counter as Peripheral Contents 1 Counter as Peripheral (9 points, total) Computer-driven Load* Switch, to Clear Counter (2 points) Counter Control Hardware: Count*/Hold (2 points) Counter Interface Hardware: Check for Overflow (3 points) Counter Interface Hardware: Read 8-bit Count (2 points) CodetoUsetheCounterHardware(6 points) 4 Total points: 15. Due Thursday, April 16, 2015 Note we ll have a quiz next week (April 16). As usual, you re invited to bring in a one-sided cheat sheet. 1 Counter as Peripheral (9 points, total) Here we ll ask you to worry about the details of interfacing a hardware counter to the lab computer. The controller can itself count events, but a hardware counter can work much faster; that s the possible motive for rigging a circuit like this one. In life, you d probably make the counter much wider than 8 bits if you meant to use it this way; but we don t want to wear you out, right off. Specifications Here s how we d like to set up this counter: Assume that you have the use of the I/O decoder ( 139) used in your lab computer, so that ports 0..3 are decoded for you, and available. counter: a 16-bit counter exactly like the PAL counter used in your lab computer; it even includes the manual pushbutton-load circuitry of Lab D3. computer controlled operations computer can read the 8 bit counter value at port 2 (external bus) computer can read whether the counter has overflowed since it last was cleared, by reading bit 0 of port 1 (external bus) computer can clear the 8 bit counter value by sending a pulse to port 3 (external bus) that simulates a manual pushbutton-pressing, and in that event loads zeros into the counter, if keypad has been set up with a 0 value beforehand (the PAL counter offers an ASYNC Load* but not an async Clear*) computer can start or stop the 8 bit counter (not clear it) by writing a value to port 2 (external bus) 1 Revisions: correct port use (2 not zero) in #2, and add request to cler counter at end of routine ( 4/15); specify pointer inits in last subsection (4/14); add start of program, mentioned but omitted (4/12), updated (4/13).

2 Homework D10, Counter as Peripheral 2 Here s a sketch of some of the hardware; you ll need to add more: Figure 1: PAL 8-bit Counter as Input Device for Computer You may recall some details of the PAL counter that could be confusing: the P0..P7 inputs feed counter D4..D11, while the four low-order bits are grounded internally; the counter is a 16-bit device. We think that you ll find it s not hard to accommodate those facts. And here we ll try to lead you to build the hardware in stages: 1.1 Computer-driven Load* Switch, to Clear Counter (2 points) Back in Lab D3 you installed a pushbutton to drive Async LOAD*. Now we d like you to allow the computer to load the counter (we could set up zeros, and thus clear the counter, as we ve mentioned). Here s Lab D3 s LOAD pushbutton: Figure 2: Lab D3 s Counter LOAD logic: to which you ll add computer load function Problem: Show what you would add so as to allow a computer OUT3* pulse (from the 139 I/O decoder of Big Board Lab µ1, and Big Picture) to LOAD the PAL counter. Don t interfere with the operation of the existing manual LOAD function.

3 Homework D10, Counter as Peripheral Counter Control Hardware: Count*/Hold (2 points) determine whether the counter Counts or Holds (freezes, but without Clearing), by sending a value to Port Counter Interface Hardware: Check for Overflow (3 points) determine whether the counter has overflowed since the last time it was Loaded (an action that effects a RESET). Let the computer determine this by reading the data bus, data line 0, at port Counter Interface Hardware: Read 8-bit Count (2 points) take in the 8-bit count from the PAL counter.

4 Homework D10, Counter as Peripheral 4 2 Code to Use the Counter Hardware (6 points) Here is the beginning of a program to use the counter. We have set up pointers for you, using the form. They point to ports 2 and 1, as you ll see in the listing below. The rest is up to you. This partial-code is posted. Don t wear yourself out typing it in! Here s what we d like your code to do: It is a subroutine, a little standalone program that will be invoked by other programs; it terminates with the RET operation. It should save any registers it messes up, by putting them on the stack. It then should recover them before returning. And here s what the routine should do: stop the counter; check for an overflow; Hint: if you bring the I/O byte into the accumulator, you can do almost any operation on it; out in I/O space, you don t have much control, using if there is an overflow, store BBh (BB hexadecimal) in a RAM location named OVERFLOWFLAG, and then return; put that location wherever you find convenient (it can be in the external RAM, or in the micro s internal RAM. If it uses the internal RAM, then you can use MOV rather than MOVX, and more addressing modes are open to you). if there is no overflow, read the 8-bit value, and save it in a RAM location named NOW COUNT. That location, too, you can put where you like. clear the counter for next pass; then return ; CNTR_RD_MT_APR12.a51 HW exercise: code to use 8-bit counter hardware $NOSYMBOLS ; keeps listing short, lest... $INCLUDE (C:\MICRO\8051\RAISON\INC\REG320.INC) ;...this line might produce huge list ; of symbol defintions (all 51 registers) ; here we ll store the data OVERFLOWFLAG DATA 010h ; a location for this variable NOW_COUNT DATA 011h ;...and another dedicated location TROUBLE EQU 0BBh ; this is a value we ll store in case of overflow ; (You needn t use this symbol, if you don t want to) ; Next lines remind us of the neat DPTR alternative; but you can use DPTR if you like ; POINTER USE: instead of DPTR, let P2 hold the high address, let R0, R1 form ; low address of two ports: ; port 2 (8002h) uses R0: serves to START/STOP counter on output ; serves to read counter data on input ; port 1 (8001h) uses R1: ;serves to LOAD/CLEAR counter on output; ; serves to check for OVERFLOW on input ORG 0 ; tells assembler the address at which to place this code LJMP TRY_ROUTINE ; here code begins--with just a jump to start of

5 Homework D10, Counter as Peripheral 5 ; real program. ALL our programs will start thus ORG 0C0h ;...and here the program starts TRY_ROUTINE: MOV SP, #07Fh ; ok place to put stack pointer (though not required) MOV P2, #080h ; init high byte of I/O address MOV R0, #002h ; init low byte of one pointer MOV R0, #001h ; init low byte of a second pointer GETCOUNT: ACALL COUNTER_READ ; this is the empty "Main" program, ; which invokes the COUNTER_READ routine SJMP GETCOUNT ;...over and over hwd10xb apr15.tex;april 9, 2015

ENSC E-123: Final Exam: Digital Electronics. Spring 2014

ENSC E-123: Final Exam Spring 2014 1 ENSC E-123: Final Exam: Digital Electronics. Spring 2014 YOUR NAME: This is a mostly-closed-book test. You may use the following materials: 1. a one-page, one-sided