7
FN4153.7
September 26, 2008
Figure 2 shows a typical application of the HA456 with
HFA1412 quad, gain-of-two buffers at the outputs to drive
75Ω loads. This application shows the HA456 digital-switch
control interface set up in the 7-bit parallel mode. The HA456
uses 7 data lines and 3 control lines (WR, CE
and LATCH).
The input/output information is presented to the chip at A2:0
and D3:0 by a parallel printer port. The data is stored in the
Master Registers on the rising edge of WR. When the
LATCH line goes high, the switch configuration loads into the
Slave Registers, and all 8 outputs reconfigure at the same
time. Each 7-bit word updates only one output at a time.
If several outputs are to be updated, the data is individually
loaded into the Master Registers. Then, a single LATCH
pulse can reconfigure all channels simultaneously.
An IBM compatible PC loads the programming data into the
HA456 via its parallel port (LPT1) using a simple BASIC
program.
TABLE 1. PARALLEL INTERFACE COMMANDS
A2:0 D3:0 ACTION
Selects
Output
Being
Programmed
0000 to 0111 Connect the input defined by D3:0 to the output selected by A2:0. Doesn’t enable a disabled output.
1000 Connect the output selected by A2:0 to GND. Doesn’t enable a disabled output.
1011 Asynchronously disable the single output selected by A2:0, and leave the Master Register unchanged.
1100 Asynchronously enable the single output selected by A2:0, and leave the Master Register unchanged.
Address
Inputs are
Irrelevant for
These
Functions
1101 Asynchronously disable all outputs, and leave the Master Register unchanged.
1110 Asynchronously enable all outputs, and leave the Master Register unchanged.
1111 Send a Software “Latch” pulse to the Slave Register to load it from the Master Register, iff, the LATCH input = 1.
If the LATCH input = 0, then this command is a NOP. The Master Register is unchanged by this command.
1001 or 1010 Do not use these codes in the parallel programming mode. These codes are for serial programming only.
TABLE 2. SERIAL INTERFACE COMMANDS
D3:0 ACTION
0000 to 0111 Connect the output to the input channel defined by D3:0. Doesn’t enable a disabled output.
1000 Connect the output to GND. Doesn’t enable a disabled output.
1001 Enable the output and connect it to GND. The default power-up state is all outputs disabled, so use this code to enable
outputs after power is applied, but before programming the switch configuration.
1010 Disable the output. The output is no longer associated with any input channel; the desired input must be redefined after
re enabling the output.
1011 to 1111 Do not use these codes in the serial programming mode.
TABLE 3. DEFINITION OF DATA AND ADDRESS BIT FUNCTIONS
SER/PAR D3 D2 D1 D0 A2:0 COMMENT
HXXSerial Data
Output
Serial Data Input X 32-Bit Serial Mode
LHParallel Data
Input
Parallel Data
Input
Parallel Data
Input
Output
Address
Parallel Mode; D2:0 define the
command to be executed
LLParallel Data
Input
Parallel Data
Input
Parallel Data
Input
Output
Address
Parallel Mode; D2:0 define the Input
Channel
HA456
