Rainbow Electronics AT73C502 User Manual

Page 16

AT73C500

Figure 11. Contents of a data package

AT73C500 offers some time for the processor to analyze
the synchronization, status and mode information before
starting to supply the measurement results. The 12 mea-
surement bytes are written on every 11th clock period.

Four handshake signals are provided, ADDR1, RD/WR,
STROBE and BRDY, for interfacing with the microproces-
sor. ADDR1 is always taken high when AT73C500 is either

writing to µP bus or reading the bus contents. When used
with slow peripheral, the BRDY input of AT73C500 can be
used to hold the device in write mode until the processor
has finished reading the bus. However, the total length of
one data package should always be less than 300 clock
cycles of AT73C500. Longer I/O periods may result errone-
ous measurement results.

Figure 12. Handshake signals of the DSP

Following the falling edge of BRDY, the data can be
strobed into the µP by the rising edge of the STROBE sig-
nal. If the microprocessor is able to read data continuously,
BRDY can be kept constantly low. Also BRDY should be
low whenever DATRDY is inactive allowing AT73C500
freely use its buses.

To avoid conflicts, the processor should always keep its
bus in tri-state mode, unless it is used to write calibration
coefficients to AT73C500.

Sync LS

Sync MS

Mode

Status

Data 1

Data 2

Data 11

Measurement data, 12 bytes

Synchronisation data

Status data

Data 12

200 clock cycles

45 clock cycles

143 clock cycles

LATCHED
DATRDY

CLK

STROBE

RWSU

ASU

RWH

BRS

CLK

DATA
FROM DSP

BRDY

STROBE

ADDR1

RD/WR

SDLY

DDLY