7267-112612-3

Counter Mode Registers: XCMR and YCMR

The CNTR operational mode is programmed by writing into the CMRs.

7 6 5 4 3 2 1 0

0 : Binary count

: Normal count

: Range Limit

: Non-recycle count

: Modulo-N

CMR

1 : BCD count

0

0

1

1

: Quadrature X1

0

: Non-quadrature

: Quadrature X2

1

: Quadrature X4

1

0: Select CMR addressed by X/Y input

1: Select both XCMR and YCMR together (Note: D7=1 overrides X/Y input)

: Select CMR

0

0

1

0

1

1

0

1

1

0

0

DEFINITIONS OF COUNT MODES:

Range Limit. In range limit count mode, an upper and a lower limit is set, mimicking limit switches in the me-

chanical counterpart. The upper limit is set by the content of the PR and the lower limit is set to be 0. The

CNTR freezes at CNTR = PR when counting up and at CNTR = 0 when counting down. At either of these limits,

the counting is resumed only when the count direction is reversed.

Non-Recycle. In non-recycle count mode, the CNTR is disabled, whenever a count overflow or underflow takes

place. The end of cycle is marked by the generation of a Carry (in Up Count) or a Borrow (in Down Count). The

CNTR is re-enabled when a reset or load operation is performed on the CNTR.

Modulo-N. In modulo-N count mode, a count boundary is set between 0 and the content of PR. When counting

up, at CNTR = PR, the CNTR is reset to 0 and the up count is continued from that point. When counting down,

at CNTR = 0, the CNTR is loaded with the content of PR and down count is continued from that point.

The modulo-N is true bidirectional in that the divide-by-N output frequency is generated in both up and down di-

rection of counting for same N and does not require the complement of N in the UP instance. In frequency di-

vider application, the modulo-N output frequency can be obtained at either the Compare (FLG1) or the Borrow

The information included herein is believed to be

accurate and reliable. However, LSI Computer Systems,

Inc. assumes no responsibilities for inaccuracies, nor for

any infringements of patent rights of others which may

result from its use.