Texas Instruments TMS380C26 - Manual (Page 11)

TMS380C26
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SPWS010A–APRIL 1992–REVISED MARCH 1993
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11
Terminal Functions (continued)
System Interface – Intel Mode (SI/M = H)
PIN NAME NO. I/O DESCRIPTION
SRAS/SAS 39 I/O
System Memory Address Strobe (see Note 3). This pin used to latch the SCS, SRSX – SRS2 register
input signals. In a minimum-chip system, SRAS is tied to the SALE output of the System Bus. The
latching capability can be defeated since the internal latch for these inputs remains transparent as
long as SRAS remains high. This permits SRAS to be pulled high and the signals at the SCS,
SRSX – SRS2, and SBHE to be applied independently of the SALE strobe from the system bus.
During DMA this pin remains an input.
High = transparent mode
Low = Holds latched values of SCS, SRSX–SRS2, and SBHE
Falling edge = latches SCS, SRSX – SRS2, and SBHE
SRD/SUDS 61 I/O
System Read Strobe (see Note 3). Active-low strobe indicating that a read cycle is performed on the
system bus. This pin is an input during DIO and an output during DMA.
H = Read cyle is not occurring.
L
= If DMA: host provides data to system bus.
If DIO: SIF provides data to system bus.
SRDY/SDTACK 60 I/O
System Bus Ready (see Note 3).The purpose of this signal is to indicate to the bus master that a data
transfer is complete. This signal is asynchonous, but during DMA and pseudo-DMA cycles it is
internally synchronized to SBCLK. During DMA cycles, it must be asserted before the falling edge
of SBCLK in state T2 in order to prevent a wait state. This signal is an output when the TMS380C26
is selected for DIO, and an input otherwise.
H = System bus NOT ready.
L
= Data transfer is complete; system bus is ready.
SRESET 25 IN
System Reset. This input signal is activated to place the TMS380C26 into a known initial state.
Hardware reset will put most of the TMS380C26 output pins into a high-impedance state and place
all blocks into the reset state. DMA bus width selection is latched on the rising edge of SRESET.
H = No system reset.
L = System reset.
Rising edge = Latch bus width for DMA operation.
SRSX
SRS0
SRS1
SRS2/SBERR 28
27
26
33
IN
System Register Select. These inputs select the word or byte to be transferred during a system DIO
access. The most significant bit is SRSX and the least significant bit is SRS2 (see Note 1).
MSb LSb
Registered selected = SRSX SRS0 SRS1 SRS2/SBERR
SWR/SLDS 40 I/O
System Write Strobe (see Note 3). This pin serves as an active-low write strobe. This pin is an input
during DIO and an output during DMA.
H = Write cycle is not occurring.
L
= If DMA: data to be drivien from SIF to host bus.
If DIO: on the rising edge, the data is latched and written to the selected register.
SXAL 42 OUT
System Extended Address Latch. This output provides the enable pulse used to externally latch the
most significant 16 bits of the 32-bit system address during DMA. SXAL is activated prior to the first
cycle of each block DMA transfer, and thereafter as necessary (whenever an increment of the DMA
address counter causes a carry-out of the lower 16 bits). Systems that implement parity on addresses
can use SXAL to externally latch the parity bits (available on SPL and SPH) for the DMA address
extension.
NOTES: 1. Pin has an internal pullup device to maintain a high voltage level when left unconnected (no etch or loads).
3. Pin should be tied to VCC with a 4.7-k
Ω
pullup resistor.