Signal Connection Considerations

Recall that when QS = 0, both queues are disabled; when QS = 8, queue 1 is active and queue 2 is idle; and when QS = 4; queue 1 is paused and queue 2 is disabled.

CONVERSION TIME = 14 QCLKS

TIME BETWEEN TRIGGERS

CONVERSION TIME = 14 QCLKS

QCLK

 

TRIG1

 

EOC

 

QS

0

CWP

LAST

CWPQ1

LAST

Q1 RES

8

4

 

CCW0

CCW0

R0

 

8

CCW1

CCW2

 

CCW1

 

R1

Figure 27-46. External Positive Edge Trigger Mode Timing with Pause

A time separator is provided between the triggers and the end of conversion (EOC). The relationship to QCLK displayed is not guaranteed.

CWPQ1 and CWPQ2 typically lag CWP and only match CWP when the associated queue is inactive. Another way to view CWPQ1 and CWPQ2 is that these registers update when EOC triggers the write to the result register.

For the CCW with the pause bit set (CCW0), CWP does not increment until triggered. For the CCW with the pause bit clear (CCW1), the CWP increments with the EOC.

The conversion results Q1 RESx show the result associated with CCWx, such that R0 represents the result associated with CCW0.

Figure 27-47shows the timing for conversions in externally gated single-scan with same assumptions in example 1 except:

No pause bits set in any CCW

Externally gated single scan mode for Q1

Single scan enable bit (SSE1) is set.

When the gate closes and opens again, the conversions start with the first CCW in Q1.

MOTOROLA

Chapter 27. Queued Analog-to-Digital Converter (QADC)

27-65

Page 649
Image 649
Motorola MCF5281, MCF5282 user manual External Positive Edge Trigger Mode Timing with Pause