AT&T 3B2/300 Technical Reference Manual page 511

FUNCTIONAL D E S C R I P T I O N - - - - - - - - - - - - - - - - - - - - - - - - - - -
Peripheral Control and Status Register
The CM521A Card contains a 16-bit Peripheral Control and Status Register (PCSR) used to control
and monitor certain CM521A functions. The CM521A Card PCSR bits are defined in the following
table.
CM521A PERIPHERAL CONTROL AND ST A TUS REGISTER
BIT DESCRIPTION
15 BYTE WRITE POINTER: PCSR15[1] points to the FIFO, FIFO O or 1, in which the next byte
of data will be written. PCSR15 is incremented after each access by hardware. PCSR15 is
zeroed by activating the 80186 Microprocessor Peripheral Chip Select 3 (PSC3).
14
BYTE READ POINTER: PCSR14[1] points to the FIFO, FIFO O or 1, from which the next
byte of data will be read. PCSR14 is incremented after each access by hardware. PCSR14 is
zeroed by activating the 80Cl86 Microprocessor Peripheral Chip Select 2 (PSC2).
13
BYTE EMPTY IND I CA TOR: PCSR13[1] indicates if the FIFO pointed to by the Byte Read
Pointer 'is empty. The 80C186 Microprocessor checks PCSR13 before attempting to read data
from the FIFO. If PCSR13 is set, data read from the FIFO by the 80C186 Microprocessor is
invalid.
12
BYTE FULL IND I CA TOR: PCSR12[1] indicates if the FIFO pointed to by the Byte Write
Pointer is full. The 80C186 Microprocessor checks PCSR12 before attempting to write data to
the FIFO. If PCSR12 is set, data written to the FIFO by the 80C186 Microprocessor is lost.
11
WORD FULL FLAG 1: PCSRl 1[0] is used to indicate if the FIFO containing the most
significant byte is full. Additional writes to the word side of the FIFO by the 80Cl86
Microprocessor while PCSRl 1 is set results in lost data.
10
WORD FULL FLAG 0: PCSRlO[O] is used to indicate if the FIFO containing the least
significant byte is full. Additional writes to the word side of the FIFO by the 80Cl86
Microprocessor while PCSRlO is set results in lost data.
09
WORD EMPTY FLAG 1: PCSR09(0] is used to indicate if the most significant byte of the
word side of the FIFO is available. PCSR09 is polled prior to an 80C186 Microprocessor read
of the word side of the FIFO.
08 WORD EMPTY FLAG 0: PCSR08[0] is used to indicate if the least significant byte of the
word side of the FIFO is available. PCSR08 is polled prior to an 80C186 Microprocessor read
of the word side of the FIFO.
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