LTC1196 datasheet(25/28 Pages) LINER

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LTC1196/LTC1198

APPLICATI

TYPICAL

Software Description

The software configures and controls the serial port of the

TMS320C25.

The code first sets up the interrupt and reset vectors. On

reset the TMS320C25 starts executing code at the label

INIT. Upon completion of a 16-bit data transfer, an inter-

rupt is generated and the DSP will begin executing code at

the label RINT.

In the beginning, the code initializes registers in the

TMS320C25 that will be used in the transfer routine. The

interrupts are temporarily disabled. The data memory

page pointer register is set to zero. The auxiliary register

pointer is loaded with one and auxiliary register one is

loaded with the value 200 hexadecimal. This is the data

memory location where the data from the LTC1198 will be

stored. The interrupt mask register (IMR) is configured to

recognize the RINT interrupt, which is generated after

receiving the last of 16 bits on the serial port. This interrupt

is still disabled at this time. The transmit framing synchro-

nization pin (FSX) is configured to be an output. The F0 bit

of the status register ST1, is initialized to zero which sets

up the serial port to operate in the 16-bit mode.

Next, the code in TXRX routine starts to transmit and

receive data. The DIN word is loaded into the ACC and

shifted left eight times so that it appears as in Figure 18.

This DIN word configures the LTC1198 for CH0 with

respect to CH1. The DIN word is then put in the transmit

repeated 3 times to mask out the interrupts and minimize

the cycle time of the conversion to be 20 clock cycles. All

clocking and CS functions are performed by the hardware.

The timing diagram of Figure 16 was obtained from the

circuit of Figure 15. The CLK was 5MHz for the timing

diagram and the TMS320C25 clock rate was 40MHz.

Figure 17 shows the timing diagram with the LTC1198

running off a 2.7V supply and 5MHz CLK.

CLK

DIN

Figure 16. Scope Trace the LTC1198 Running Off

5V Supply in the Circuit of Figure 15

CLK

DIN

Figure 18. DIN Word in ACC of TMS320C25 for the

Circuit in Figure 15

HORIZONTAL: 1500ns/DIV

1196/98 F16

LSB

(B0)

HORIZONTAL: 500ns/DIV

1196/98 F17

Figure 17. Scope Trace the LTC1198 Running Off

2.7V Supply in the Circuit of Figure 15

NULL

BITS

MSB

(B7)

LSB

(B0)

NULL

BITS

MSB

(B7)

L1196/98 F18

B15

START

S/D

O/S

DUMMY

DOUT

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