EM6520 EM Microelectronic, EM6520 Datasheet - Page 18

• Manufacturer Part Number: EM6520
• Description: MFP version of EM6620 Ultra Low Power Microcontroller 4x8 LCD Driver
• Manufacturer: EM Microelectronic

6.4.2 Pull-up/Down
For each terminal of PB[3:0] an internal input pull-up (metal mask MPBPU[n]) or pull-down (metal mask
MPBPD[n]) resistor are connected per metal mask option (ROM version only). Per default the two resistors are
in place. In this case one can chose per software to have either a pull-up, a pull-down or no resistor. See below.
For Metal mask selection and available resistor values refer to chapter 16.1.2.
Pull-down ON : MPBPD[n] must be in place ,
Pull-down OFF : MPBPD[n] is not in place,
Pull-up ON *
Pull-up OFF*
Never can pull-up and pull-down be active at the same time.
For POWER SAVING one can switch off the port B pull resistors between two read phases. No cross current
flows in the input amplifier while the port B is not read. The recommended order is :
Minimum time with current on the pull resistor is 4 periods of the system clock, if the RC constant is lower than 1
system clock period. Adding a NOP before reading moves the number of periods with current in the pull resistor
to 6 and the maximum RC delay to 3 clock periods.
6.4.3 CMOS / NCH. Open Drain Output
The port B outputs can be configured as either CMOS or Nch. open drain outputs. In CMOS both logic ‘1’ and ‘0’
are driven out on the terminal. In Nch. open drain only the logic ‘0’ is driven out on the terminal, the logic ‘1’ value
is defined by the internal pull-up resistor or high impedance.
If using the Dynamic Input Comparator one must put the PB[0] in CMOS input mode and should not use any pull
resistor on this terminal. If not doing so the device may draw excessive current.
EM Microelectronic-Marin SA CH-2074 Marin, Switzerland, Tel. [phone], Fax. [phone]
18
Figure 12. CMOS or Open Drain outputs
F re q u e n c y
O u tp u ts
D R [n ]
• switch on the pull resistor.
• allow sufficient time - RC constant - for the pull resistor to drive the line to either V
• Read the port B
• Switch off the pull resistor
AND the bit NoPdPB [n] must be ‘0’ .
OR if MPBPD[n] is in place NoPdPB [n] = ‘1’ cuts off the pull-down.
OR selecting NchOpDPB [n] = ‘1’ cuts off the pull-down.
AND the bit NchOpDPB [n] must be ‘1’ ,
AND the bit PBIOCntl[n] = ‘0’ (input mode) OR if PBIOCntl[n] = ‘1’ while PBData [n] = 1.
OR if MPBPU[n] is in place NchOpDPB [n] = ‘0’ cuts off the pull-up,
OR if MPBPU[n] is in place and if NchOpDPB [n] = ‘1’ then PBData[n] = 0 cuts off the pull-up.
M U X
C M O S O u tp u t
: MPBPU[n] must be in place,
: MPBPU[n] is not in place,
D a ta
T ri-S ta te O u tp u t
B u ffe r : c lo s e d
1
T e rm in a l
P B [n ]
I / O
F re q u e n c y
O u tp u ts
D R [n ]
N c h . O p e n D ra in O u tp u t
M U X
© EM Microelectonic-Marin SA , 12/98 Rev. A/246
T ri-S ta te O u tp u t
B u ffe r : H ig h
Im p e d a n c e fo r
D a ta = 1
A COMPANY OF
EM6520
SS
A c tiv e P u llu p
fo r H ig h S ta te
or V
T e rm in a l
P B [n ]
DD
I / O
.