
EM6517
FOR ENGINEERING ONLY
EM Microelectronic-Marin SA, 09/99, Rev. A/277
18
For Metal mask selection and available resistor values refer to 19.1.2. (mask selections are valid for ROM
versions only)
Pull-down ON
: MPBPD[n] must be in place ,
AND
bit
NoPdPB
[n] must be ‘0’ .
Pull-down OFF
: MPBPD[n] is not in place,
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.
Pull-up ON
:
MPBPU[n] must be in place,
AND
bit
NchOpDPB
[n] must be ‘1’ ,
AND
(bit
PBIOCntl[n]
=
‘0’ (input mode)
OR
if
PBIOCntl[n]
=
‘1’ while
PBData
[n] = 1. )
Pull-up OFF
: MPBPU[n] is not in place,
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 the pull-up.
Never pull-up and pull-down can 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 :
Switch on the pull resistor.
Allow sufficient time - RC constant - for the pull resistor to drive the line to either V
SS
or V
DD
.
Read the port B
Switch off the pull resistor
Minimum time with current on the pull resistor is 4 system clock periods, if the RC time constant is lower than 1
system clock period. Adding a NOP instruction before reading moves the number of periods with current in the
pull resistor to 6 and the maximum RC delay to 3 clock periods.
7.4.3 CMOS or Nch. 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 on the terminal, the logic ‘1’
value is defined by the internal pull-up resistor (if implemented), or high impedance.
Figure 14. CMOS or Nch. Open Drain Outputs
I / O
Term inal
PB[n]
M UX
Active Pull-up
for High State
PBData[n]
Frequency
O utputs
Tri-State O utput
Buffer : High
Im pedance for
Data = 1
I / O
Term inal
PB[n]
M UX
PBData[n]
Frequency
O utputs
Tri-State O utput
Buffer : closed
Data
1
CM OS Output
Nch. Open Drain O utput