8

The difference between the Async 16 mode and the Async

24 mode is the number of data bits available to the user. In

16-bit mode, the user can connect the system data bus to

the lower 16 bits of the Histogrammer’s DIO bus. The UWS

pin becomes the LSB of the IO address, which determines if

the lower 16 bits or upper 8 bits of the 24-bit Histogrammer

data is being used. When UWS is low, the data present at

DIO0-15 is the lower 16 bits of the data in the IOADD0-9

location. When UWS is high, the upper 8 bits of the

IOADD09 location are present on DIO0-7. (This is true for

both reading and writing). Thus, it takes 2 cycles for an

asynchronous 24-bit operation when in Async 16 mode.

Unused outputs are zeros.

ADDRESS

GENERATOR

24x1024

IN

OUT

ADDRESS

DIO 0-23

UWS

CONTROL

WR

DIO

I/F

RAM

RD

WR

IOADD 0-9

FIGURE 14. ASYNCHRONOUS 16/24 BLOCK DIAGRAM

WR

IOADD 0-9,

RD

DIO 0-23

READ CYCLE TIMING

WR

IOADD 0-9,

RD

DIO 0-23

WRITE CYCLE TIMING

UWS

UWS

FIGURE 15. ASYNCHRONOUS 16/24 MODE TIMING

HSP48410