8

LTC1598

Microprocessor Interfaces

The LTC1598 can interface directly (without external hard-

ware) to most popular microprocessors’ (MPU) synchro-

nous serial formats including MICROWIRE

QSPI. If an MPU without a dedicated serial port is used,

then three of the MPU’s parallel port lines can be pro-

grammed to form the serial link to the LTC1598. Included

here is one serial interface example.

Motorola SPI (MC68HC05)

The MC68HC05 has been chosen as an example of an MPU

with a dedicated serial port. This MPU transfers data MSB-

register starts the SPI process. With three 8-bit transfers

the A/D result is read into the MPU. The second 8-bit

transfer clocks B11 through B7 of the A/D conversion

result into the processor. The third 8-bit transfer clocks

the remaining bits B6 through B0 into the MPU. ANDing

least significant bit. Shifting the data to the right by one bit

results in a right justified word.

MC68HC05 CODE

LDA #$52

Configuration data for serial peripheral

control register (Interrupts disabled, output

enabled, master, Norm = 0, Ph = 0, Clk/16)

STA $0A

Load configuration data into location $0A (SPCR)

LDA #$FF

Configuration data for I/O ports

(all bits are set as outputs)

STA $04

Load configuration data into Port A DDR ($04)

STA $05

Load configuration data into Port B DDR ($05)

STA $06

Load configuration data into Port C DDR ($06)

LDA #$08

(CH0 with respect to GND)

STA $50

START BSET 0,$02

Bit 0 Port C ($02) goes high (CS goes high)

LDA $50

STA $0C

start clocking data

LOOP1 TST $0B

Test status of SPIF bit in SPI status register ($0B)

BPL LOOP1 Loop if not done with transfer to previous

instruction

BCLR 0,$02

Bit 0 Port C ($02) goes low (CS goes low)

LDA $0C

Load contents of SPI data register into Accumulator

STA $0C

Start next SPI cycle

LOOP2 TST $0B

Test status of SPIF

BPL LOOP2 Loop if not done

LDA $0C

Load contents of SPI data register into Accumulator

STA $0C

Start next SPI cycle

AND #$IF

STA $00

Load Port A ($00) with MSBs

LOOP3 TST $0B

Test status of SPIF

BPL LOOP3 Loop if not done

LDA $0C

Load contents of SPI data register into Accumulator

AND #$FE

STA $01

Load Port B ($01) with LSBs

JMP START Go back to start and repeat program

MICROWIRE is a trademark of National Semiconductor Corp.