1999 Jan 08
17
Philips Semiconductors
Product specification
Enhanced Pager Decoder for POCSAG
PCD5003A
Fig.8 Message types.
(a) Master writes to slave.
(b) Master reads from slave.
(c) Combined format (shown: write plus read).
handbook, full pagewidth
n bytes with acknowledge
FROM
MASTER
FROM
SLAVE
A
A
S
SLAVE ADDRESS
R/W
DATA
A
DATA
A
P
S = START condition
P = STOP condition
A = Acknowledge
N = Not acknowledge
n bytes with acknowledge
A
S
SLAVE ADDRESS
R/W
DATA
DATA
P
A
(a)
(b)
(c)
R/W
DATA
SL. ADR.
SL. ADR.
R/W
DATA
0 (write)
0 (write)
1 (read)
1 (read)
index
address
index
address
n bytes with
acknowledge
n bytes with
acknowledge
change of direction
N
A
A
A
INDEX
INDEX
A
S
S
N
P
MLC250
7.25
Decoder I
2
C-bus access
All internal access to the PCD5003A takes place via the
I
2
C-bus interface. For this purpose the internal registers,
SRAM and EEPROM have been memory mapped and are
accessed via an
index register
. Table 13 shows the index
addresses of all internal blocks.
Registers are addressed directly, while RAM and
EEPROM are addressed indirectly via address pointers
and I/O registers.
Remark
: The EEPROM memory map is non-contiguous
and organized as a matrix. The EEPROM address pointer
contains both row and column indicators.
Data written to read-only bits will be ignored. Values read
from write-only bits are undefined and must be ignored.
Each I
2
C-bus write message to the PCD5003A must start
with its slave address, followed by the index address of the
memory element to be accessed. An I
2
C-bus read
message uses the last written index address as a data
source. The different I
2
C-bus message types are shown in
Fig.8.
As a slave the PCD5003A cannot initiate bus transfers by
itself. To prevent an external controller from having to
monitor the operating status of the decoder, all important
events generate an external interrupt on output INT.