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| P R E L I M I N A R Y | AMD |
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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
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 |