Philips Semiconductors Product data sheet
SC28L91
3.3 V or 5.0 V Universal Asynchronous
Receiver/Transmitter (UART)
2004 Oct 21 15
UnitMaxTypMinParameterSymbol
Receiver Timing, external clock (See Figure 13)
t*RXS RxD data setup time to RxC high 50 10 ns
t*RXH RxD data hold time from RxC high 50 10 ns
68000 or Motorola bus timing (See Figures 6, 7, 8)10
tDCR DACKN Low (read cycle) from X1 High10 18 57 ns
tDCW DACKN Low (write cycle) from X1 High 18 57 ns
tDAT DACKN High impedance from CEN or IACKN High 10 15 ns
tCSC CEN or IACKN setup time to X1 High for minimum DACKN cycle 30 10 ns
NOTES:
1. Parameters are valid over specified temperature and voltage range.
2. All voltage measurements are referenced to ground (GND). For testing, all inputs swing between 0.4 V and 3.0 V with a transition time of
5 ns maximum. For X1/CLK this swing is between 0.4 V and 0.8*VCC. All time measurements are referenced at input voltages of 0.8 V and
2.0 V and output voltages of 0.8 V and 2.0 V, as appropriate.
3. Test conditions for outputs: CL = 125 pF, except open drain outputs. Test conditions for open drain outputs: CL = 125 pF,
constant current source = 2.6 mA.
4. Typical values are the average values at +25 °C and 3.3 V.
5. T iming is illustrated and referenced to the WRN and RDN Inputs. Also, CEN may be the “strobing” input. CEN and RDN (also CEN and
WRN) are ORed internally. The signal asserted last initiates the cycle and the signal negated first terminates the cycle.
6. Guaranteed by characterization of sample units.
7. If CEN is used as the “strobing” input, the parameter defines the minimum High times between one CEN and the next. The RDN signal must
be negated for tRWD to guarantee that any status register changes are valid.
8. Minimum frequencies are not tested but are guaranteed by design.
9. Clocks for 1X mode should maintain a 60/40 duty cycle or better.
10.Minimum DACKN time is tDCR = tDSC + tDCR + two positive edges of the X1 clock. For faster bus cycles, the 80XXX bus timing may be used
while in the 68XXX mode. It is not necessary to wait for DACKN to insure the proper operation of the SC28C91. In all cases the data will be
written to the SC28L91 on the falling edge of DACKN or the rise of CEN. The fall of CEN initializes the bus cycle. The rise of CEN ends the
bus cycle. DACKN low or CEN high completes the write cycle.