P R E L I M I N A R Y

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3–0

A2DT[3:0]

1010b

A/D sampling Time[3:0]. The value in the A2DT[3:0] field deter-

mines the duration of time required to convert the A/D input. Each bit of resolution is equal to 4 times the CLKIN period when the CLKGT20 bit of MIR9 is set to 0 and is equal to 8 times the CLKIN period when the CLKGT20 bit of MIR9 is set to 1. For a 1Mbs data rate with CLKIN = 20 MHz and CLKGT20 = 0, the resolution is 200 n. The A2DT value is used by all A/D modes, including the mode that uses the internal A/D converter. The internal A/D converter requires 600 nsec to convert – note that the default value of this reg- ister is 2.0 μs for a CLKIN equal to 20MHz with the CLKGT20 bit set to 0.

Note that the actual time for conversion is less than the A2DT pro- grammed value by 1.5 CLKIN periods (with CLKGT20=0, it is 3 CLKIN periods if CLKGT20=1). This fact is important when using an external A/D converter in the external A/D mode.

Minimum value in the A2DT[3:0] field must be 0001. A value of 0000 is not allowed.

ANTSLT

CCA_TEST (Internal Signal)

START_A2D (Internal Signal)

CACT=TIR27[7]

SAR[￿6:0] When ENSAR = 1

ADIN1 (when ENEXT=1)

ADIN2 (when ENEXT=1)

SAR_LATCH (Internal Signal)

ADT[5:0]=TCR4[5:0]

3 X tA

SS[5:0]=TCR24[5:0]

A2DT[3:0]=TCR25[3:0]+4 X tA

2 X tA

tA

1 X tA

6 X tA

3 X tA

6 X tA

3 X tA

tA = period of CLKIN when CLKGT20 = 0 tA = (period of CLKIN) X 2 when CLKGT20 = 1

20138B-9

Note: ADIN1, ADIN2, and SAR_LATCH signals are only valid as shown when ENEXT (TCR25[6]) has been set to a 1.

Figure 3. Analog-to-Digital State Machine Timing

Am79C930

119

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Image 119
AMD manual Analog-to-Digital State Machine Timing Am79C930 119, CACT=TIR277