Apple Lisa - Device Protocol

Confidential
Lisa Hardware Reference Manual
DEVICE PROTOCOL
To enable the boot ROM to boot the system at power on from an
expansion device, every I/O card must conform to certain
identification and control protocols. Each card must contain a small
ROM Which identifies the card to the boot ROM. If the card has a
boot program, the program also must be contained in this ROM. The
I/O card's ROM is addressed as the lowest significant byte of the SLn
select for the card. The ROM contents are:
I/O CARD m AND BOOT ROM
+------+
Address 1
I
type code (bsnn nnnn
nnnn
nnnn)
3
I
I
-+
b-bootable, s·status,
5
I
byte count
I
7
I I
+--
-+
9
I
boot program
I
I
data
I
•
I
I • - -+
n I checksum I
I • ----+
The type code is a 16 bit female byte sex number (most significant·
byte first) stored in the first two bytes of the ROM. If the first
bit is a 1 (see above), the device claims to be bootable. If the
device's status should be checked at boot time, its status bit (the
second bit) is a 1. The other 14 bits are the identification number
which
identifies the card.
Before the boot ROM executes the card's boot program, it loads
register Al with the address of the first word of SLn for the
expansion slot. The boot program can therefore access the card by
addressing relative to Al.
If the status bit is on, the status program, Which can contain device
setup code, should begin at the first word of the program data. The
boot program, if present, should begin at the third word of the data.
The status program should always return to the boot ROM leaving its
result in register DO. A result of 0 indicates that the device is
happy. The boot ROM checks each card's status bit and executes the
status program, as required. It then checks parameter memory to
decide which device to try to boot from, and checks that device's
boot bit to insure that a boot program is present.
Page 57
7-Jul-81
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