
SAB 82532/SAF 82532
Microprocessor Interface
Semiconductor Group
42
07.96
3
Microprocessor Interface
3.1
The communication between the CPU and the ESCC2 is done via a set of directly
accessible registers. The interface may be configured as Siemens/Intel or Motorola type
with a selectable data bus width of 8 or 16 bits.
The CPU transfers data to/from the ESCC2 (via 64 byte deep FIFOs per direction and
channel), sets the operating modes, controls function sequences, and gets status
information by writing or reading control/status registers. All accesses can be done as
byte or word accesses if enabled. If 16-bit bus width is selected, access to lower/upper
part of the data bus is determined by address line A0 and signal BHE/BLE as shown in
table 1
and
2
.
Register Set
Mixed Byte/Word Access to the FIFOs
Reading from or writing to the internal FIFOs (RFIFO and XFIFO of each channel) can
be done using an 8-bit (byte) or 16-bit (word) access depending on the selected bus
interface mode. In version 1 of ESCC2, byte access in the case of 16-bit bus interface
mode is allowed if not mixed with word accesses when reading from or writing to the
same pool.
In version 2.x upward randomly mixed byte/word access to the FIFOs is allowed with the
restriction that in HDLC mode and BISYNC mode 32 bytes have to be written to the
internal FIFO when only XTF (HDLC) command or XF (BISYNC) command is set
afterwards. There is no restriction when XTF and XME (HDLC) or XF and XME
(BISYNC) is set afterwards.
Table 1
Data Bus Access (16-bit Intel mode)
BHE
A0
Register Access
0
0
FIFO word access
Register word access (even addresses)
0
1
Register byte access (odd addresses)
1
0
Register byte access (odd addresses)
1
1
No transfer performed
ESCC2 Data Pins Used
D0 … D15
D8 … D15
D0 … D7
None