MK50H28N ST Microelectronics, Inc., MK50H28N Datasheet - Page 17

• Manufacturer Part Number: MK50H28N
• Description: Multi Logical Link Frame Relay Controller
• Manufacturer: ST Microelectronics, Inc.

SECTION 4
PROGRAMMING SPECIFICATION
This section defines the Control and Status Reg-
isters and the memory data structures required to
program the MK50H28.
4.1 Control and Status Registers
There are six Control and Status Registers
(CSR’s) resident within the MK50H28.
CSR’s are accessed through two bus address-
able ports, an address port (RAP), and a data
port (RDP), thus requiring only two locations in
the system memory or I/O map.
4.1.1.1 Register Address Port (RAP)
15:08
06:04
03:01
BIT
07
00
RESERVED Must be written as zeroes
RESERVED Must be written as zeroes
CS3<2:0>
1
5
0
HBYTE
NAME
BM8
1
4
0
0
1
3
When set, places chip into 8 bit mode. CSR’s, Init Block, and data transfers are all 8 bit
transfers; this provides compatibility with 8 bitmicroprocessors. When clear, all transfers
are 16 bit transfers. This bit must be set to the same value each time it is written,
changing this bit during normal operation will achieve unexpected results. BM8 is
READ/WRITE and cleared on Bus RESET.
CSR address select bits. READ/WRITE. Selects the CSR to be accessed through the
RDP. RAP is cleared by Bus RESET.
Determines which byte is addressed for 8 bit mode. If set, the high byte of the register
referred to by CSR<2:0> is addressed, otherwise the low byte is addressed. This bit is
only meaningful in 8 bit mode and must be written as zero if BM8=0. HBYTE is
READ/WRITE and cleared on bus reset.
1
2
0
1
1
0
1
0
0
CSR<2:0>
0
0
9
0
1
2
3
4
5
The
0
8
0
0
7
M
4.1.1 Accessing the Control and Status Regis-
ters
The CSR’s are read (or written) in a two step op-
eration. The address of the CSR is written into the
address port (RAP) during a bus slave transac-
tion. During a subsequent bus slave transaction,
the data being read from (or written into) the data
port (RDP) is read from (or written into) the CSR
selected in the RAP. Once written, the address in
RAP remains unchanged until rewritten or upon a
bus reset. A control I/O pin (ADR) is provided to
distinguish the address port from the data port.
B
8
CSR0
CSR1
CSR2
CSR3
CSR4
CSR5
CSR
DESCRIPTION
0
6
0
ADR
0
5
0
Port
0
0
4
0
3
<2:0>
CSR
0
2
0
1
H
B
Y
T
E
0
0
MK50H28
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