AD7859/AD7859L
REV. A
–24–
DATA
VALID
DATA
VALID
t16
t15
t17
t14
t13
tCONVERT
t1
t18
t5
t6
t7
t8
t9
*W/B PIN LOGIC HIGH
BUSY
CS
WR
DB0 – DB15
CONVST
RD
INTERNAL
DATA
LATCH
OLD DATA
NEW DATA
Figure 35. Read and Write Cycle Timing Diagram for 16-Bit Transfers
Figure 35 shows the read cycle timing diagram for 16-bit trans-
fers for the AD7859. When operated in word mode, the HBEN
input does not exist, and only the first read operation is required
to access data from the AD7859. Valid data, in this case, is pro-
vided on DB0–DB15. When operated in byte mode, the two
read cycles shown in Figure 36 are required to access the full data
word from the AD7859. Note that in byte mode, the order of
successive read operations is important when reading the cali-
bration registers. This is because the register file address pointer
is incremented on a high byte read as explained in the calibra-
tion register section of this data sheet. In this case the order of
the read should always be Low Byte–High Byte. In Figure 36,
the first read places the lower 8 bits of the full data word on
DB0–DB7 and the second read places the upper 8 bits of the
data word on DB0–DB7.
The CS and RD signals are gated internally and level-triggered
active low. In either word or byte mode, CS and RD may be
tied together as the timing specification for t5 and t6 is 0 ns min.
The data is output a time t8 after both CS and RD go low. The
RD
rising should be used to latch data by the user and after a
time t9 the data lines will become three-stated.
PARALLEL INTERFACE
The AD7859 provides a flexible, high speed, parallel interface.
This interface is capable of operating in either word (with the
W/B pin tied high) or byte (with W/B tied low) mode. A detailed
description of the different interface arrangements follows.
Reading
With the W/B pin at a logic high, the AD7859 interface operates
in word mode. In this case, a single read operation from the
device accesses the word on pins DB0 to DB15 (for a data read,
the 12-bit conversion result appears on DB0–DB11). DB0 is
the LSB of the word. The DB8/HBEN pin assumes its DB8
function. With the W/B pin at a logic low, the AD7859 interface
operates in byte mode. In this case, the DB8/HBEN pin as-
sumes its HBEN function. Data to be accessed from the
AD7859 must be accessed in two read operations with 8 bits of
data provided by the AD7859 on DB0–DB7 for each of the
read operations. The HBEN pin determines whether the read
operation accesses the high byte or low byte of the 16-bit word.
For a low byte read, DB0 provides the LSB of the 16-bit word.
For a high byte read DB0 provides data bit 8 of the 16-bit word
with DB7 providing the MSB of the 16-bit word.
t3
t4
t3
t4
t5
t10
t6
t7
t8
t9
LOW BYTE
HIGH BYTE
*W/B PIN LOGIC LOW
HBEN
CS
RD
DB0 – DB7
Figure 36. Read Cycle Timing for Byte Mode Operation