SC28C94 Philips Semiconductors, SC28C94 Datasheet - Page 34

• Manufacturer Part Number: SC28C94
• Description: Quad universal asynchronous receiver/transmitter QUART
• Manufacturer: Philips Semiconductors

bidding interrupt scheme, it is entirely safe to use. In fact it is setting
used for normal reading and writing to the QUART (the generation of
Philips Semiconductors
through the most significant 6 bits. The result of this is that the
channel value does not ’bid’. However the logic is such that other
parts of the bid being equal the condition of the highest channel will
be captured in CIR. The increasing order of the channels is A, B, C,
D. Thus channel D is the ”strongest” of the four.
It could be that the giving the highest strength to channel D may,
from time to time, not be what would be most desired. Further it
may be desired to alter the authority of a channel’s bid. This may
be done by setting the Rx and/or Tx interrupt bits in MR0 and MR1
to values different than zero. This will have the effect of not allowing
the associated receiver or transmitter to bid until its FIFO reaches a
particular fill level. Although this compromises the idea of the
of MR0 and MR1 interrupt bits to zero that causes the receiver to
stop bidding when it is empty and causes the transmitter to stop
bidding when it is full. Altering the MR0 and MR1 interrupt bits only
changes the level at which the Rx & Tx bidding is stopped.
Table 10.
NOTE ON QUART INTERFACE TO ITS
CONTROLLING PROCESSOR
The QUART, has been designed to interface in either the
synchronous interrupt environment (without DACKN) or the
asynchronous interrupt environment (with DACKN). The 80xxx
devices of Intel design are usually operated in a synchronous
interrupt mode while those of Motorola design, 68xxx devices,
operate in an asynchronous interrupt mode.
Note: Synchronous and asynchronous interrupt modes are not
in any way associated with synchronous or asynchronous data
transmission.
The QUART has been designed with the pins required to service
either interface. In general then it is probable that in any application
some of the interface pins will not be used. This note discusses
what is required for the ”text book” connections of the two methods.
It should be noted that features of either method are not mutually
exclusive.
The interface pins are all active low. (at V
a bus cycle) are CEN (Chip Enable), RDN (Read Enable), WRN
1998 Aug 19
Interrupt vector for
Interrupt vector for
Interrupt vector for
Interrupt vector for
ICR[1 0] 11 (I hibit)
ICR[1:0]=11 (Inhibit)
Quad universal asynchronous receiver/transmitter (QUART)
ICR[1 0] 00
ICR[1:0]=00
ICR[1 0] 01
ICR[1:0]=01
ICR[1 0] 10
ICR[1:0]=10
Configuration of Interrupt Vector for the QUART
BIT 7
Interrupt vector 3 MSBs
Rx or Tx byte count
SS
IVR[7:5]
or ground) The pins
BIT 6
INTERRUPT VECTOR FORMATS (Controlled by ICR[1:0])
Interrupt threshold ICR[7:2]
CURRENT INTERRUPT REGISTER FORMAT CIR[7:0]
INTERRUPT CONTROL REGISTER FORMAT ICR[0:7]
Interrupt vector 6 MSBs
BIT 5
IVR[7:2]
Inhibit vector output. (Set bus to FFh)
34
BIT 4
Full interrupt vector
Interrupt type: R/Tx CT COS BRK
In normal operation the character of an interrupt will be controlled by
Register (one for each DUART)) . The function of the IMR will be to
loops for the service routines and find the addition of several tests of
During a read of the QUART DACKN signals that valid data is on the
See the “Interrupt Note on 28C94” which refers to the use of the MR
registers in controlling the Rx and Tx bidding.
the above registers in conjunction with the IMR (Interrupt Mask
enable bidding of any particular source. Recall that the QUART has
18 functions which may generate an interrupt.
The format of the interrupt vector is controlled by the ICR[1:0] bits.
The formats are shown in Table 10. The purpose of the vector
modification is to allow the interrupting source (either channel or
type and channel) to direct the processor to appropriate service
routine. We have found that some users wish to use extremely tight
status bytes to be very ’expensive’ in processor time.
(Write Enable). The pins used in the interrupt service are IRQN
(Interrupt Request), IACKN (Interrupt Acknowledge). The pin used
for data transfer is DACKN (Data Acknowledge). IRQN and DACKN
are open drain outputs.
DACKN signaling can be enabled or disabled via writing to address
27h or 26h respectively. Note that if DACKN is enabled that writing
to the QUART will occur on the falling edge of DACKN. The use of
hardware reset (required at power up) enables DACKN.
The Asynchronous Interface
Those familiar with 68xxx I/O will note the use of the two pins RDN
and WRN to be in conflict with 68xxx devices use of the one R/WN
pin. The R/WN must be inverted such that the R/WN may drive the
WRN input while the inversion of R/WN drives the RDN input. It is
good practice to condition the inversion of R/WN such that RDN will
not become active on the termination of a write to the QUART while
CEN is still asserted. These short periods of read could upset FIFO
pointers in the chip.
data bus. During a write to the QUART DACKN signals that data
placed on the bus by the control processor has been written to the
IVR[7:0]
Interrupt type
ICR[4:2]
BIT 3
BIT 2
Interrupt vector format
BIT 1
Channel number
Channel number
Channel number
Product specification
SC28C94
ICR[1:0]
ICR[1:0]
ICR[1:0]
BIT 0