EM6517 datasheet(21/64 Pages) EMMICRO

21 / 64 page

EM6517

03/02 REV. C/448

 2002, EM Microelectronic-Marin SA

www.emmicroelectronic.com

For Metal mask selection and available resistor values refer to chapter 19.1.3. (metal mask selection only valid

for Rom version

)

Pull-down ON

: MPCPD[n] must be in place ,

AND

bit NoPdPC[n] must be ‘0’ .

Pull-down OFF

: MPCPD[n] is not in place,

if MPCPD[n] is in place NoPdPC[n] = ‘1’ cuts off the pull-down.

selecting NchOpDPC[n] = ‘1’ cuts off the pull-down.

Pull-up ON

: MPCPU[n] must be in place,

AND

bit NchOpDPC[n] must be ‘1’ ,

AND

(bit PCIOCntl = ‘0’ (input mode) OR if PBIOCntl = ‘1’ while PCData[n] = 1. )

Pull-up OFF

: MPCPU[n] is not in place,

if MPCPU[n] is in place NchOpDPC[n] = ‘0’ cuts off the pull-up,

if MPCPU[n] is in place and if NchOpDPC[n] = ‘1’ then PCData[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 C pull resistors between two read phases. No cross current

flows in the input amplifier while the port C 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 VSS or VDD.

• Read the port C

• 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.

7.6.2 CMOS or Nch. Output

The port C 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.

In CMOS output mode the pad can be driven high or low. Pull-ups and pull-downs are not active.

In CMOS input mode, if the corresponding metal option is in place (default), one can choose to have an internal

pull-down resistor by setting to “1“ the bit NoPdPC in OPTPCandStr register (default pull-down).

In N-Channel open drain mode, if the corresponding metal option is in place (default), one always has the pull-

up resistor active except if the port is in output mode and drives a "0" (RegPCCntl= "1", RegPBData[n]= "0") The

pull-down resistor is always off in Nch. open drain mode.

Pull-downs in CMOS input mode and weak pull-ups in Nch. open drain mode are port-wise configurable with the

be different for each port C terminal.

Figure 16. CMOS or Nch. Open Drain Outputs

I / O

T e rm inal

PC [n ]

MU X

Ac tiv e Pu ll-u p

fo r H ig h S ta te

P C D a ta [n ]

T ri-S tate O u tput

B u ffer : H igh

Im pedanc e fo r

Da ta = 1

I / O

T e rm inal

PC [n ]

P CDa ta [n ]

T ri-S tate O u tput

B u ffer : c los ed

C M OS Ou tp u t

N c h. O pen D rain O u tput

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