Modes Of Operation - IBM RT Series Hardware Reference Manual

Modes of Operation
The different modes of operation are selected by programming the NS 16450 asynchronous
communications element. This is done by selecting the 110 address and writing data out to the 1/0
address. Address bits AO, A1, and A2 select the different registers that define the modes of
operation. Also, the divisor latch access bit (bit 7) of the line control register is used to select
certain registers.
The address range for this adapter is X'1230' through X'4247'. Figure 5 and Figure 6 on page 6
depict a value of n, which represents a variable determined by the setting of switch bank two ..
Switches 1, 2, 3, and 4 of switch bank two allow the card to operate and select the appropriate
address range.
110 Decode (In Hex)
PortH PortA Register Selected DLAB State
n238 n230 TX Buffer DLAB=O (Write)
n238 n230 RXBuffer DLAB=O (Read)
n238 n230 Divisor Latch LSB DLAB=1
n239 n231 Divisor Latch MSB DLAB=1
n239 n231 Interrupt Enable Register
DLAB=O
n23A n232 Interrupt Identification
Register
n23B n233 Line Control Register
n23C n234
Modem Control Register
n23D n235 Line Status Register
n23E n236 Modem Status Register
Figure 5.
II
0 Decodes, Port A and Port B
Notes:
1. n is equal to the first digit of the adapter address range
2. DLAB means Divisor Latch Access Bit.
5080 Peripheral Adapter 5