psd4235g2 STMicroelectronics, psd4235g2 Datasheet - Page 64

• Manufacturer Part Number: psd4235g2
• Description: Flash In-system Programmable Isp Peripherals For 16-bit Mcus 5v Supply
• Manufacturer: STMicroelectronics

Complex PLD (CPLD)
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Loading and Reading the output macrocells (OMC)
The output macrocells (OMC) block occupies a memory location in the MCU address space,
as defined by the CSIOP (see
macrocells (OMC) can be loaded from the data bus by a MCU. Loading the output
macrocells (OMC) with data from the MCU takes priority over internal functions. As such,
the preset, clear, and clock inputs to the flip-flop can be overridden by the MCU. The ability
to load the flip-flops and read them back is useful in such applications as loadable counters
and shift registers, mailboxes, and handshaking protocols.
Data is loaded to the output macrocells (OMC) on the trailing edge of Write Strobe
(WR/WRL, CNTL0).
The OMC Mask register
There is one Mask register for each of the two groups of eight output macrocells (OMC). The
Mask registers can be used to block the loading of data to individual output macrocells
(OMC). The default value for the Mask registers is 00h, which allows loading of the output
macrocells (OMC). When a given bit in a Mask register is set to a '1,' the MCU is blocked
from writing to the associated output macrocells (OMC). For example, suppose McellA0-
McellA3 are being used for a state machine. You would not want an MCU WRITE to McellA
to overwrite the state machine registers. Therefore, you would want to load the Mask
register for McellA (Mask macrocell A) with the value 0Fh.
The output Enable of the OMC
The output macrocells (OMC) can be connected to an I/O port pin as a PLD output. The
output enable of each port pin driver is controlled by a single product term from the AND
Array, ORed with the Direction register output. The pin is enabled upon Power-up if no
output enable equation is defined and if the pin is declared as a PLD output in PSDsoft
Express.
If the output macrocell (OMC) output is declared as an internal node and not as a port pin
output in the PSDabel file, then the port pin can be used for other I/O functions. The internal
node feedback can be routed as an input to the AND Array.
Section 20: I/O
ports). The flip-flops in each of the 16 output
PSD4235G2