EE 308 Exam 3 Solutions

EE 308
Exam 3
Solutions

The figure below shows a simple address decoding scheme for a 68HC11.
1. For what address range will output Y2 be selected? Will it be used as a chip select for an input or output port?
```
A15 A14 A13 = 1 1 1
        A12 = 0
A11 A10 R/W = 0 1 0

Addr = 1110 01XX XXXX XXXX, R/W = 0

Addr = 0xE400 - 0xE7FF    Output
```
2. For what address range will output Y5 be selected? Will it be used as a chip select for an input or output port?
```
A15 A14 A13 = 1 1 1
        A12 = 0
A11 A10 R/W = 1 0 1

Addr = 1110 10XX XXXX XXXX, R/W = 1

Addr = 0xE800 - 0xEBFF    Input
```
3. Write a C-language #define statement which will access data in a peripheral connected to output Y5:
```
     #define EXP_Y5 (* (unsigned char *) 0xE800)
```

The figure below shows a 68XYZ Super Terrific Universal Peripheral Interface Device (STUPID) chip connected to a 68HC11 with a 2 MHz E clock.

What range of addresses will select the STUPID chip?

A15 A14 A13 = 1 0 0
A10 A11 A12 = 0 1 0

Addr = 1000 10XX XXXX XXXX

Addr = 0x8800 - 0x8BFF

compatible with the 68HC11? Why or why not? What is the corresponding time for the 2 MHz 68HC11?

From Figure A-14 of the Technical Data Manual, corresponding time is 3 - 19,
or 222 ns - 128 ns = 94 ns.  
HC11 puts data on bus 94 ns before E goes high, STUPID needs it 80 ns before,
so time is compatible.

compatible with the 68HC11? Why or why not? What is the corresponding time for the 2 MHz 68HC11?

From Figure A-14 of the Technical Data Manual, corresponding time is 21 - 9,
or 33 ns - 33 ns = 0 ns. 
HC11 removes data and address at same time, STUPID needs address on 50 ns
after data removed, so time is not compatible.

compatible with the 68HC11? Why or why not? What is the corresponding time for the 2 MHz 68HC11?

From Figure A-14 of the Technical Data Manual, corresponding time is 12,
or 94 ns.
HC11 puts address on bus 94 ns before E goes high, STUPID needs address on
140 ns before E goes high, so time is not compatible.

compatible with the 68HC11? Why or why not? What is the corresponding time for the 2 MHz 68HC11?

From Figure A-14 of the Technical Data Manual, corresponding time is 9,
or 33 ns.
HC11 holds address on bus 33 ns after E goes low, STUPID needs address on
held for 20 ns before E goes low, so time is compatible.

Explain in words what

means.

This is the amount of time STUPID needs valid data on bus before E goes low.

The figure below shows two 68HC11s connected by their 6821 PIA ports.
1. How do you clear flags on the MC6821?
```
Read the port for which the flag is set.  For example, if IRQA1 is set,
read EXP_PORTA.
```
2. Write some C code which will set up PIA Port B on the master HC11 so that:
  - The master PIA Port B is an output.
  - The master CB1 is an input, active on the falling edge, with interrupt disabled.
  - The master CB2 is an output, goes low on a write to PIA Port B, and goes back high on the next E clock.
```
EXP_CRB  = 0x00;   /* Access DDRB */
EXP_DDRB = 0xff;   /* Make Port B output */
EXP_CRB  = 0x2c;   /* CB2 control = 101; DDRB access = 1; CB1 control = 00 */
```
3. Write some C code which will set up PIA Port A on the slave HC11 so that:
  - The slave PIA Port A is an input.
  - The slave CA1 is an input, active on the falling edge, with interrupt enabled.
  - The slave CA2 is an output, goes low on a read from PIA Port A, and goes back high on the next E clock.
```
EXP_CRA  = 0x00;   /* Access DDRA */
EXP_DDRA = 0x00;   /* Make Port A input */
EXP_CRA  = 0x2d;   /* CA2 control = 101; DDRA access = 1; CA1 control = 01 */
```
4. Write some C code for the master which will write a byte to the slave and wait for the slave to acknowledge receipt of the data.
```
temp = EXP_PORTB;             /* Make sure flag clear by reading port */
EXP_PORTB = data;             /* Write data to port */
while ((CRB & 0x80) == 0) ;   /* Wait for acknowledgement */
```

The figure below shows an SOTC-001 Super Oven Temperature Controller connected to a 68HC11 by its SPI. The SOTC-001 works in the folowing manner: the HC11 selects the SOTC-001, then sends it an 8-bit number (from 0

C to 255

C) which tells the SOTC-001 what temperature to set the oven at. It then reads a byte from the SOTC-001, which tells the HC11 the actual temperature of the oven. The HC11 then deselects the SOTC-001. The figure shows the SPI timing information. The maximum SCK the SOTC-001 can use is 250 kHz.

How do you clear the SPI flag?

Read SPSR, then read from or write to SPDR.

Write some C code to set up the 68HC11 SPI for use with the SOTC-001. Be sure to set up DDRD and SPCR correctly, and explain what the bits you set in SPCR do.

DDRD |= 0x38;     /* SS, SCK, MOSI outputs; must do this before setting up */
                  /*   SPCR */
SPCR  = 0x56;     /* SPE = 1, MSTR = 1 */
                  /* CPHA = 1 -- Data stable on 2nd clock edge */
                  /* CPOL = 0 -- latch data on falling edge */
                  /* SPR[1:0] = 10 -- 125 kHz clock (fastest compatible with */
                  /*   SOTC-001 */

Write some C code to set the oven temperature at 198

C, and read the actual oven temperature.

PORTD |= 0x20;      /* Select SOTC-001 */
temp = SPSR;        /* First step in clearing SPIF */
SPDR = 198;         /* Writes to SOTC-001 and finishes clearing SPIF */
while ((SPSR & 0x80) == 0) ;  /* Wait for transfer to finish */
SPDR = 0x00;        /* Write dummy byte to SOTC-001 to get SCK going; */
                    /*   Also clears SPIF */
while ((SPSR & 0x80) == 0) ;  /* Wait for transfer to finish */
oven_temp = SPDR;   /* Read oven temperature from SOTC-001 */
PORTD &= ~0x20;     /* Deselect SOTC-001 */