BU21026MUV Datasheet, PDF (14/23 Pages) Rohm – 4-wire Resistive Touch Screen Controller

BU21026MUV
A/D Conversion Time
When MAF is disabled, an A/D conversion takes 66 internal core clocks (CCLK) with 12-bit mode and 38 CCLK with 8-bit
mode. When MAF is enabled, it takes 476 CCLK with 12-bit mode and 244 CCLK with 8-bit mode. In MAF mode, the
number of sampling becomes 7. So the A/D conversion cycles become large.
The A/D conversion clocks and time are shown in Table 5. The number of CCLK and time are counted from a stop or
repeated start condition after sending a conversion command. In this table, the time is calculated by CCLK is 4MHz in
typically.
MAF
Enable
Disable
Table 5. A/D Conversion Time (CCLK = 4MHz)
MODE NUMBER OF CCLK
TIME [us]
12-bit
476
119.0
8-bit
244
61.0
12-bit
66
16.5
8-bit
38
9.5
A/D Sampling Time with 2-wire Serial Interface
The master need to send a conversion command and a read command for getting an A/D converted data. So, a throughput
rate is affected by 2-wire serial interface frequency. Each write cycle takes 20 SCL and each read cycle takes 29 SCL
(12-bit mode) or 20 SCL (8-bit mode). Note that each a start and a stop condition take 1 SCL in this count.
When the 2-wire serial interface frequency is 400 KHz, one period become 2.5us. Each A/D sampling time takes 241.5us
(49 x 2.5 us + 119.0 us) with 12-bit mode and MAF. So, a control throughput rate becomes 4.14 kSPS. In MAF mode,
BU21026MUV operates A/D conversion 7 times. It means that an operation throughput rate is increased 7 times. It
becomes 28.99 kSPS.
2-WIRE SERIAL
INTERFACE
FREQENCY
100 kHz
(10us period)
400 kHz
(2.5us period)
MAF
Enable
Disable
Enable
Disable
Table 6. Control and Operation Throughput
MODE
NUMBER
OF SCL
A/D
CONVERSION
TIME [us]
CYCLE TIME
[us]
12-bit
49
8-bit
40
12-bit
49
8-bit
40
12-bit
49
8-bit
40
12-bit
49
8-bit
40
119.0
61.0
16.5
9.5
119.0
61.0
16.5
9.5
609.0
461.0
506.5
409.5
241.5
161.0
139.0
109.5
CONTROL
THROUGHPUT
[kSPS]
1.64
2.17
1.97
2.44
4.14
6.21
7.19
9.13
OPERATION
THROUGHPUT
[kSPS]
11.49
15.18
-
-
28.99
43.48
-
-
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TSZ22111 • 15 • 001
14/19
TSZ02201-0L5L0FF00890-1-2
4.Aug.2016 Rev.001