TT DCU FUNCTIONAL DESCRIPTION

Incarnations:  National ???
          Styra ST-4130

Pin Description
The DCU (data control unit) is a combination of a bi-directional
4 to 1
mux and a double buffered latch. It is used to interface the 32
bit
system data bus to the 8 bit peripheral chip controlled by the TT
DMAC.

D0-D31    TTL bi-dir     system data bus

PD0-PD7   TTL bi-dir     peripheral data bus

XCEN CMOS input     enables the D0-D31 pins as outputs

XPEN CMOS input     enables the PD0-PD7 pins as outputs

XLDI CMOS input     latches the state of the D0-D31 and
               PD0-PD7 pins when low

XHOLD     CMOS input     closes the secondary latches in the
               double buffer when low

XLWRD     CMOS input     causes the lower 16 bits of the latches
               to be gated onto the upper 16 bits. Used
               when CPU reads latch contents as a word.

XTHRU     CMOS input     causes the latches to be bypassed. Used
               to pass data directly thru the chip.

DA0,DA1   CMOS inputs    control which byte of the long word is
               envolved in a latching operation. The
               8 bit data from the PDx lines can be latched
               in one of four latches. Used to assemble
               bytes from the peripheral into long words
               or to select bytes from a long word to go to
               the peripheral.

S16X8     CMOS input     selects which 8 of the Dx lines are used
               for pass thru operations. Should be tied
               high in the TT.

Package:
The circuit has 49 signal pins. The package is a 68 pin PLCC.
Bonding diagram to be supplied by the ASIC vendor.

Pin Out
1  - XCEN 18 - D7        35 - D20  52 - PD1
2  - XPEN 19 - D8        36 - D21  53 - PD2
3  - XLDI 20 - D9        37 - D22  54 - PD3
4  - XHOLD     21 - D10  38 - D23  55 - PD4
5  - XLWRD     22 - D11  39 - D24  56 - PD5
6  - XTHRU     23 - D12  40 - D25  57 - PD6
7  - VSS  24 - D13  41 - D26  58 - PD7
8  - VDD  25 - VSS  42 - VSS  59 - VSS
9  - VDD  26 - VDD  43 - VDD  60 - VDD
10 - VSS  27 - VDD  44 - VDD  61 - VDD
11 - D0        28 - VSS  45 - VSS  62 - VSS
12 - D1        29 - D14  46 - D27  63 - NC
13 - D2        30 - D15  47 - D28  64 - NC
14 - D3        31 - D16  48 - D29  65 - NC
15 - D4        32 - D17  49 - D30  66 - DA0
16 - D5        33 - D18  50 - D31  67 - DA1
17 - D6        34 - D19  51 - PD0  68 - S16X8

There are no internal registers in the DCU.