Scan Operation - NEC VR4181 mPD30181 User Manual

16.2.4 Scan operation

Scan operations are controlled by the T1CNT(4:0) and T3CNT(4:0) bits of the KIUWKS register and the
WINTVL(9:0) bits of the KIUWKI register. The following diagram illustrates the relationship of these register bits to the
scan operation:
T1CNT(4:0) + 1
Hi-Z
SCANOUT0
(output)
Hi-Z
SCANOUT1
(output)
Hi-Z
SCANOUT2
(output)
Hi-Z
SCANOUT3
(output)
Hi-Z
SCANOUT4
(output)
Hi-Z
SCANOUT5
(output)
Hi-Z
SCANOUT6
(output)
Hi-Z
SCANOUT7
(output)
The T1CNT(4:0) bits specify the keyboard settling time and is expressed in 32.768 kHz clock cycles. Following the
low level of one of the SCANOUT(7:0) pins, the KIU will wait for the time set in the T1CNT(4:0) bits before reading
returned data to the SCANIN(7:0) pins. Actually the SCANOUT pins will be driven as low for (T1CNT(4:0) + 1) 32.768
kHz clock cycles.
The T3CNT(4:0) bits specify the delay from driving one SCANOUT pin as high impedance to driving the next
SCANOUT pin as low and is also expressed in 32.768 kHz clock cycles. When the SCANOUTn pin is driven as high
impedance, the KIU will wait for the time set in the T3CNT(4:0) bits before driving the SCANOUTn+1 pin as low to
allow the external pull-up resistors to return the SCANINn pin as high (n = 0 to 6).
The WINTVL(9:0) bits specify the interval between one scan and another in 32.768 kHz clock cycles. After the last
SCANOUT pin has been driven as high impedance and a time set in the T3CNT(4:0) bits has elapsed, the KIU will
wait for the time set in the WINTVL(9:0) bits before driving SCANOUT0 as low to start the next scan sequence.
CHAPTER 16 KEYBOARD INTERFACE UNIT (KIU)
Figure 16-1. SCANOUT Signal Output Timing
Hi-Z
T3CNT(4:0)
Hi-Z
Hi-Z
Hi-Z
User's Manual U14272EJ3V0UM
Hi-Z
Hi-Z
Hi-Z
WINTVL(9:0)
T3CNT(4:0)
Hi-Z
Hi-Z
Hi-Z
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